Fixed focal length objective lens

Abstract

To more satisfactorily correct longitudinal chromatic aberration of a fixed focal length objective lens. The objective lens has a fixed focal length, a front lens group (VG) that is fixed in the optical direction, a fixed aperture (BL) with an adjustable aperture, a fixed rear lens group (HG), and a focusing group (MG) that is shiftable relative to the aperture along the optical axis of the objective lens for imaging objects at a plurality of different distances onto a fixed image plane (IM), the focusing group (MG) consisting of at least one lens element and a diffractive optical element (DOE) incorporated in the focusing group (MG).

Description

[Technical Field]

[0001] The invention relates to a fixed focal length objective lens having the features of the preamble (preamble) of claim 1. [Background technology]

[0002] Such objectives are known in various forms and with different focal lengths. By shifting the focusing group, the structural (mechanical) length of the objective is not changed. This type of focusing is therefore called inner focusing, but the focusing group can be arranged in front of (upstream of) the diaphragm in the light direction (seen in the light direction) or behind (downstream of) the diaphragm, i.e., can be shifted relative to the diaphragm.

[0003] From the publication US Pat. No. 9,201,213 B2 an imaging objective is known which has inner focusing and a single lens as the focusing element.

[0004] From the publication US 2006 / 0 082 882 A1, a single lens with a DOE (diffractive optical element) for achromatic imaging with an extended depth of focus is known.

[0005] From the publication US 2002 / 003 660 A1 a diffractive-refractive lens doublet as an achromatic imaging lens is known.

[0006] From the publication US 2015 / 002 939 A1, a fixed lens element with a DOE in the front group of the objective lens is known, where a cemented lens element is provided for focusing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US 9,201,213 B2 [Patent Document 2] US 2006 / 0 082 882 A1 [Patent Document 3] US 2002 / 003 660 A1 [Patent Document 4] US 2015 / 002 939 A1 Summary of the Invention [Problem to be solved by the invention]

[0008] Furthermore, it is known that objectives having focusing elements that can be moved independently of one another require extensive and therefore expensive mechanical control mechanisms, especially electromechanical control mechanisms in the case of autofocus objectives. In order to ensure the movement of both focusing elements along the optical axis of the objective, such objectives are made relatively large.

[0009] Therefore, in order to reduce the structural length of the objective lens, it is desirable to integrate the focusing elements into a single focusing group, which preferably consists of only one lens. To achieve nearly satisfactory color correction when using a single lens, such focusing elements are often made of low-dispersion glass (phosphate glass), but such glass is particularly sensitive to environmental influences during the manufacturing process. Therefore, cemented elements are often provided to improve the correction of monochromatic and chromatic aberrations. In the case of objective lenses for large formats, such as small or medium formats, focusing cemented elements are heavy and move slowly, resulting in particularly slow autofocus.

[0010] The imaging performance of such an objective is not satisfactory due to the longitudinal chromatic aberration (error) of the process (Gang) over the distance adjustment range.

[0011] Therefore, the object of the present invention is to make it possible to better correct longitudinal chromatic aberrations (longitudinal color errors) in order to be able to minimize imaging errors during this process over the distance adjustment range. Furthermore, it is desirable to significantly reduce the mass of the focusing element in order to be able to achieve rapid movements for autofocus use. [Means for solving the problem]

[0012] This problem is solved according to the invention in an objective lens of the type mentioned in the introduction by the features of claim 1. That is, the present invention 1st A fixed focal length objective lens is provided, which comprises three optical structural groups, including a front lens group that is fixed in the optical direction, a fixed aperture with an adjustable aperture, a fixed rear lens group, and a focusing group that is shiftable relative to the aperture along the optical axis of the objective lens for imaging objects at a plurality of different distances onto a fixed image plane, wherein the focusing group is composed of at least one lens element and a diffractive optical element incorporated in the focusing group. The ratio of the overall focal length of the focusing group to the overall focal length of the objective lens is 0.9 at minimum and 3.0 at maximum. The focusing group is composed of a single lens element having an aspherical convex front surface in the light direction, and the rear surface has a vertex radius configured to be substantially planar. The ratio of the overall focal length of the focusing group to the vertex radius is -0.1255 at minimum and 0.1388 at maximum. The diffractive optical element is disposed on the substantially planar rear surface. (Form 1). Furthermore, according to a second aspect of the present invention, there is provided an objective lens with a fixed focal length composed of three optical structural groups, including a front lens group that is fixed in the optical direction, a fixed aperture with an adjustable aperture, a fixed rear lens group, and a focusing group that is shiftable relative to the aperture along the optical axis of the objective lens for imaging objects at a plurality of different distances onto a fixed image plane, characterized in that the focusing group is composed of at least one lens element and a diffractive optical element incorporated therein, the ratio of the overall focal length of the focusing group to the overall focal length of the objective lens is at least 0.5 and at most 1.0, the focusing group is composed of a single lens element having an aspherical convex front surface in the optical direction, the rear surface having a weakly curved apex radius that is at least 1.013 mm when the overall focal length is normalized to 1 mm, and the diffractive optical element is disposed on the weakly curved rear surface (Function 5). Furthermore, according to a third aspect of the present invention, there is provided an objective lens with a fixed focal length composed of three optical structural groups, including a front lens group that is fixed in the optical direction, a fixed aperture with an adjustable aperture, a fixed rear lens group, and a focusing group that is shiftable relative to the aperture along the optical axis of the objective lens for imaging objects at a plurality of different distances onto a fixed image plane, characterized in that the focusing group is composed of at least one lens element and a diffractive optical element incorporated in the focusing group, and the focusing group is composed of two lens elements arranged sequentially behind the aperture in the optical direction, the first of the two lens elements having an aspherical convex front surface and the second of the two lens elements having the diffractive optical element disposed on its planar rear surface (form 8). DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a preferred embodiment of the present invention will be described. (Mode 1) See the first aspect of the present invention above. (Feature 2) In the objective lens according to feature 1, It is preferable that the front lens group has a positive focal length, and the focusing group as a whole has a positive focal length. (Feature 3) In the objective lens according to feature 1 or 2, Preferably, the ratio of the focal length of the diffractive optical element to the overall focal length of the objective lens is at least 14.9 and at most 45.4. (Feature 4) In the objective lens according to any one of Features 1 to 3, The focusing group preferably consists of only one lens element having, in the optical direction, an aspherical convex front surface and a planar rear surface on which the diffractive optical element is arranged. (Mode 5) See the second aspect of the present invention above. (Feature 6) In the objective lens according to feature 5, It is preferable that the front lens group has a positive focal length, and the focusing group as a whole has a positive focal length. (Embodiment 7) The objective lens according to embodiment 5 or 6, Preferably, the ratio of the focal length of the diffractive optical element to the overall focal length of the objective lens is at least 14.9 and at most 45.4. (Embodiment 8) See the third aspect of the present invention above. (Feature 9) In the objective lens according to feature 8, It is preferable that the front lens group has a positive focal length, and the focusing group as a whole has a positive focal length. (Mode 10) In the objective lens according to Mode 8 or 9, Preferably, the ratio of the focal length of the diffractive optical element to the overall focal length of the objective lens is at least 14.9 and at most 45.4. (Embodiment 11) The objective lens according to any one of embodiments 8 to 10, Preferably, the first lens element has a concave posterior surface and the second lens element has a convex anterior surface. (Mode 12) In the objective lens according to any one of Modes 1 to 11, Preferably, the focusing group is movable from a position having focusing on an object point at infinity to a position having close distance focusing, in a direction opposite to the direction of light, away from the rear lens group towards the front lens group. (Mode 13) In the objective lens according to Mode 12, the focusing group is disposed in a region adjacent to the aperture stop, in front of or behind the aperture stop; Preferably, there are no optical elements or at most one further optical element between the focusing group and the diaphragm. (Feature 14) In the objective lens according to any one of Features 1 to 13, The first lens of the front lens group is preferably configured with an aspherical surface on one or both sides. (Mode 15) In the objective lens according to any one of Modes 1 to 14, The final lens in the rear lens group is preferably configured with an aspherical surface on one or both sides. (Mode 16) In the objective lens according to any one of Modes 1 to 15, It is preferable that the ratio of the volume V of the focusing group to the cube of the image circle diameter on the image plane is less than 0.1. (Mode 17) In the objective lens according to any one of Modes 1 to 16, The ratio of the optical structure length of the objective lens to the image circle diameter on the image plane is 3.0 It is preferable that:

[0014] The focusing group movable for distance adjustment is made up of at least one, but at most two, commonly moving (interlocking) lens elements, each having a positive or negative refractive power and selectively having diffractive properties on the one hand and refractive properties produced by a spherical or aspherical surface on the other hand (the other), and the focusing group as a whole has a positive refractive power, and the entire objective lens focal length f' ges of diffractive optical elements focal length f' DOE The ratio is at least 14.9 and at most 45.4.

[0015] The focusing group, which is movable for distance adjustment, is arranged in the near-aperture region and is shifted in the opposite direction of the light direction (incident on the objective lens) for focusing from infinity adjustment (or setting) (in which the objective lens is focused on an object point at infinity) to focusing at close distances. In doing so, the focusing group moves away from the rear lens group towards the front lens group. The near-aperture region is defined as the region immediately before (upstream) or immediately after (downstream) the aperture, with no or at most one further optical element being arranged between the aperture and the focusing element.

[0016] Further aspects of the invention will become apparent from the features in the description of the drawings.

[0017] With regard to the solution features defined in the claims, it should be noted that modern optical design typically uses automatic correction programs, such as "CodeV" by Synopsys or "Zemax" by ZEMAX LLC., which are able to calculate a proposal for a functional objective lens system with an optimized correction state for a given task from a preset lens array and refractive power distribution. The automatically achieved correction state can be further improved each time by the optical designer's targeted modification of the specified parameters.

[0018] By virtue of the features of claim 1, this method already provides structural data on the radii, lens thicknesses, lens spacing, refractive indices and Abbe numbers of the optical glasses available. By taking into account the features of the dependent claims and drawings, the structural parameters can be improved in a targeted manner in stages.

[0019] The creation and calculation of aspheric surfaces in optical lens elements and the creation and calculation of diffractive elements are known per se to those skilled in the art with regard to their influence on the imaging light path in optical systems.

[0020] Thus, for example, aspherical surfaces can be expressed using the conic section representation of the aspherical lens as follows: It is represented by TIFF0007719181000001.tif23136. However, it is assumed that the optical axis is in the z direction, and z(h) specifies the sag height (sag amount: Pfeilhöhe) parallel to the optical axis at a distance h perpendicular to the optical axis. The aspherical coefficients a2, a4, ... an represent the deviation (amount) of the surface from an axisymmetric quadric surface, r predetermines the radius of curvature of the spherical surface, and k predetermines the Conic constant.

[0021] The geometry and calculation of the diffractive element are described by the focal length and the phase profile of the diffractive surface with respect to the spectral line with wavelength 546.0740 nm, namely the Fraunhofer line e.

[0022] The equation for the phase profile of a diffractive surface is: TIFF0007719181000002.tif1293

[0023] where Ψ doe corresponds to the phase profile at a distance h perpendicular to the optical axis, and C1, C2, C3, ..., Cn correspond to the phase coefficients.

[0024] Focal length f' of a diffractive surface for e-ray doe The formula for is: TIFF0007719181000003.tif1552

[0025] where λ constr corresponds to the structural wavelength chosen in the following examples with 546.074 nm, which is equal to the spectral line e. The diffraction order m is 1 in these examples.

[0026] The paraxial magnification β' is TIFF0007719181000004.tif1431, where n corresponds to the refractive index in front of (upstream of) the optical element, and n' corresponds to the refractive index behind (downstream of) the optical element. By definition, u corresponds to the paraxial marginal ray in front of the optical element, and u' corresponds to the paraxial marginal ray behind the optical element.

[0027] Abbe number v for e-line e with spectral lines C'=643.8469 nm, e=546.0740 nm and F'=479.9914 nm Defined by TIFF0007719181000005.tif1737.

[0028] The use of diffractive optical elements (DOEs) in photographic objectives is also known per se, with the diffractive optical elements being arranged on the lens element, for example as photolithographically produced microstructures (diffractive structures). The goal is generally to minimize chromatic aberrations while at the same time facilitating the construction of the objective. It is not known to focus on the construction of one focusing element per objective. However, this knowledge plays an important role for the construction of lightweight objectives as a whole.

[0029] In the case of objective-digital camera systems according to the invention, unwanted, stronger chromatic magnification aberrations that may occur in the variants of the objectives configured according to the invention can be corrected in the camera after the image capture by software algorithms. It is also possible to correct the image data in a computer by post-processing.

[0030] The embodiments of the present invention are illustrated in the drawings as schematic cross-sectional views of lenses and will be explained in detail with the aid of the drawings. It should be noted that the reference numerals used in the claims are intended solely to aid in understanding the invention, and are not intended to limit the claimed invention to the illustrated embodiments. [Brief explanation of the drawings]

[0031] [Figure 1] 1 shows an example of an objective lens of the present invention that is composed of a front group VG, a middle group MG, and a rear group HG, each of which has a positive overall refractive power. [Figure 2] 1 shows an example of an objective lens of the present invention that is composed of a front group VG, a middle group MG, and a rear group HG, each of which has a positive overall refractive power. [Figure 3] 1 shows an example of an objective lens of the present invention that is composed of a front group VG, a middle group MG, and a rear group HG, each of which has a positive overall refractive power. [Figure 4] 1 is an example of an objective lens of the present invention that is composed of a front group VG having a positive overall refractive power, a middle group MG having a positive overall refractive power, and a rear group HG having a negative or positive overall refractive power. [Figure 5] 1 is an example of an objective lens of the present invention that is composed of a front group VG having a positive overall refractive power, a middle group MG having a positive overall refractive power, and a rear group HG having a negative or positive overall refractive power. [Figure 6] 1 is an example of an objective lens of the present invention that is composed of a front group VG having a positive overall refractive power, a middle group MG having a positive overall refractive power, and a rear group HG having a positive overall refractive power. [Figure 7] 1 is an example of an objective lens of the present invention that is composed of a front group VG having a positive overall refractive power, a middle group MG having a positive overall refractive power, and a rear group HG having a positive overall refractive power. [Figure 8] 1 shows an example of an objective lens of the present invention that is composed of a front group VG, a middle group MG, and a rear group HG, each of which has a positive overall refractive power. [Figure 9] 1 shows an example of an objective lens of the present invention that is composed of a front group VG, a middle group MG, and a rear group HG, each of which has a positive overall refractive power. [Figure 10] An example of a circular imaging surface IM at the image position. [Example]

[0032] Generally, in the lens cross-section, lens surfaces marked with a * symbol are configured to be aspherically curved, and surfaces marked with a # symbol have diffractive power.

[0033] The possibilities for solving the problem according to the invention are not limited to the embodiments described below, which are therefore only illustrated by way of example and diagrammatically in the drawings, in which the same reference numerals in the different figures represent elements that are the same or functionally identical or that correspond in terms of their function.

[0034] The illustrated examples of inner-focusing objectives with a fixed structural length are, according to the definitions in the specification, further parameters disclosed, and claims, composed of a front lens group VG, a fixed aperture BL with an adjustable aperture, a fixed rear lens group HG, and a middle lens group MG as a focusing group that can be shifted along the optical axis of the objective relative to the aperture. In all figures, the focusing group MG is positioned in an infinity adjustment state and is supported so that it can be shifted in the direction of the arrow shown, opposite the light (incident) direction, for focusing on close object points. According to the definition, the individual lenses are numbered L1, L2, L3, ... in the light (incident) direction (as viewed). In this case, the individual lenses are grouped into groups G1, G2, G3, ...

[0035] The embodiment of the objective lens having a fixed focal length and a constant structural length shown in Figures 1 to 3 is composed of three optical structural groups, namely a front group VG, a middle group MG, and a rear group HG, each of which has a positive overall refractive power, and these are arranged in front of (at the upper end of) the image position IM when viewed in the light direction.

[0036] For normalized representation, the following figures are given as focal length ratios.

[0037] Focal length f' of the front group VG VG teeth +7.0≦f' VG / f' ges ≦+25.7 The focal length of the middle group MG is defined as MG teeth +1.6≦f' MG / f' ges ≦+3.0 and the focal length of the rear group HG is in the range of f' HG teeth +3.1≦f' HG / f' ges ≦+5.0 is in the range.

[0038] The front group VG is composed of two subgroups G1 and G2, the middle group MG is composed of one optical element G3, and the rear group HG has two subgroups G4 and G5. Between the front group VG and the middle group MG is an aperture stop BL with a variable aperture diameter. By definition, the middle group MG is located in the near-aperture region, i.e., no further optical elements are provided between the aperture stop BL and the middle group MG. The middle group MG is composed of one optical element G3 and is supported so that it can move in the direction opposite to the light direction (i.e., in the direction of the arrow) toward the aperture stop BL for focusing from the infinity position shown in the figure to the close focus distance.

[0039] In one advantageous embodiment, the refractive power f' of the middle group MG MG On the one hand, it should not be chosen too small (because otherwise the focus stroke from infinity to close-up focusing would be longer), and on the other hand, its refractive power should not be chosen too large (because otherwise the lens volume would increase). If both effects work against each other, the focusing of the objective would become too slow and would no longer be suitable for autofocus use.

[0040] Therefore, in accordance with the present invention, the focal length f' of the middle group MG teeth +1.6≦f' MG / f' ges ≦+3.0 should be selected from:

[0041] In one particularly advantageous embodiment, the optical element G3 of the middle group MG has upper and lower limits in order to minimize chromatic aberration (color error) over the entire distance adjustment range of the objective lens. +33.6≦f' DOE / f' ges ≦+45.4 Diffractive power f' in the range DOE The lens L5 has the following surface.

[0042] According to the invention, the diffractive structures required for the diffractive power can be easily manufactured on a planar (flat) or at most slightly curved surface. Thus, in one advantageous embodiment, the vertex radius (vertex curvature radius) r of the diffractive surface of the lens L5 of the middle group MG is DOE are upper and lower limits -0.1255≦f' MG / r DOE ≦+0.1388 It is flat within the range.

[0043] If the other surface of lens L5 directed towards aperture stop BL has a positive refractive power and is preferably aspherically configured, compensation of monochromatic aberrations over the distance adjustment range is ensured in an advantageous manner.

[0044] The subgroup G1 of the front group VG is composed of two elements L1 and L2, and has a negative refractive power as a whole. G1 is the range f' G1 / f' ges ≦-3.7 is defined by

[0045] At least one first convex / concave lens L1 having negative refractive power is configured in a meniscus shape and is arranged so that its concave side faces the convex side of at least one lens L2 having positive refractive power.

[0046] The subgroup G2 of the front group VG has two elements L3 and L4, which have a positive refractive power as a whole. At least one first lens L3 with negative refractive power is biconcave and is arranged with its first concave side directed toward the lens L2 of the subgroup G1. The second element of the subgroup G2 has at least one lens L4 with positive refractive power. In this embodiment, elements L3 and L4 are configured as single lenses, and together they form a doublet.

[0047] Due to the characteristics of the subgroups G1 and G2, compensation of monochromatic aberrations is advantageously carried out between the image center (the center of the image formed on the image plane by the objective lens: Bildmitte) and the image field (including the image center: Bildfeld) (at any point or position on the image plane extending from the image center to the periphery of the image plane or image field).

[0048] The subgroup G4 of the rear group HG has two elements L6 and L7 and has a positive refractive power as a whole. The subgroup G4 has at least one biconvex lens L6 with positive refractive power and at least one biconcave lens L7 with negative refractive power. L6 is positioned so that its first convex side faces the middle group MG. In this embodiment, elements L6 and L7 are each configured as a single lens, and together they are configured as a doublet.

[0049] The subgroup G5 of the rear group HG has a negative or positive overall refractive power and is composed of at least one final lens L8, the first surface of which is concave and is arranged to be directed toward the subgroup G4. In this case, the focal length f' of the subgroup G5 is G5 is the range -0.1≦f' ges / f' G5 ≦+0.1 is defined by

[0050] The characteristics of the subgroups G4 and G5 make it possible to advantageously achieve a minimization of coma, astigmatism and distortion in the image field.

[0051] Advantageously, the refractive index n of at least one of the lenses having positive refractive power in the front group VG has a value of 1.85 or greater (n≧1.85), and in this way the Petzval sum is minimized.

[0052] More advantageously, in order to further minimize the Petzval sum, the refractive index n of at least one of the lenses having positive refractive power in the rear group HG is also selected to be 1.85 or greater (n≧1.85).

[0053] An advantageously selected refractive index n of the first lens element having a negative refractive power of the front group VG of less than or equal to 1.60 (n≦1.60) also contributes to minimizing the Petzval sum.

[0054] To compensate for monochromatic aberrations in the image field, the first lens L1 of the front group VG is constructed with one or both aspherical surfaces.

[0055] Advantageously, the last lens L8 of the rear group HG is constructed with one or both aspherical surfaces in order to achieve further compensation of monochromatic aberrations in the image field.

[0056] A lightweight focusing group MG is advantageous for high focusing speed. In this case, the ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd on the image plane should be less than 0.1 (V / Bd 3 It has been found to be particularly advantageous if the focusing group has a diameter Bd < 0.1. In this way, the focusing group is made lighter, allowing for faster focusing. A lighter focusing group also has the advantage of lower power consumption when using autofocus, allowing for quieter focusing. The image circle diameter Bd is also known to those skilled in the art as the image diagonal of the digital imaging sensor Bs and is explained in more detail using FIG. 10.

[0057] For a compact structure, it is further advantageous if the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 2.0 or less (SO' / Bd≦2.0), where the optical structure length SO' is defined as the distance from the vertex of the first lens surface of the lens L1 on the optical axis in the light direction to the image position IM.

[0058] Advantageously, an objective constructed according to the above-described characteristics has a half object angle w of 31° or greater (w≧31°).

[0059] The objective lens has an aperture ratio F / # of at least 1.7 and at most 2.5, advantageously in the range 1.7 to 2.5 (1.7≦F / #≦2.5).

[0060] The objective lens shown in Figure 1 has a compact structure, and the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 1.73 (SO' / Bd=1.73), the half object angle w is 42° (w=42°), and the aperture ratio F / # is 2.0 (F / #=2.0).

[0061] In this objective lens, the small groups G1 to G5 described above are made up of lenses L1 to L8 having the following refractive power arrangement when viewed in the light (incident) direction: -+-+++--.

[0062] Given the overall focal length f' of the objective lens ges In response to the above, Focal length f' of the front group VG VG teeth f' VG / f' ges =+7.7 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+2.8 By The focal length of the rear group HG is f' HGteeth f' HG / f' ges =+3.4 It is particularly advantageous to define it as follows:

[0063] The lens L5 of the optical element G3 of the middle group MG, located behind (downstream of) the aperture stop BL, is configured as a convex lens having an aspherical first surface and a planar (flat) second surface when viewed in the direction of light. f' DOE / f' ges =+38.9 Diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. The planar second surface is particularly suitable for the simple manufacture of diffractive structures, and the aspherical first surface provides compensation of monochromatic aberrations over the entire distance adjustment range.

[0064] The subgroup G1 of the front group VG is composed of two lenses L1 and L2, and as a whole: f' G1 / f' ges =-485.6 The focal length f' G1 It has.

[0065] In this case, the first lens L1 has a convex-concave shape with negative refractive power, and is configured in a meniscus shape with a spherically curved convex side and an aspherically curved concave side.

[0066] The small group G2 of the front group VG is f' G2 / f' ges =+9.5 The focal length f' G2 It is advantageous to have

[0067] The focal lengths thus defined for the subgroups G1 and G2 ensure compensation of monochromatic aberrations between the image center and the image field.

[0068] The small group G4 of the rear group HG is composed of a biconvex lens L6 and a biconcave lens L7, which are combined to form a f' G4 / f' ges =+3.6 The focal length f' G4 The doublet is configured as

[0069] In one advantageous embodiment, the subgroup G5 of the rear group HG is f' ges / f' G5 =+0.01 The focal length f' G5 and is configured as a single lens L8 having concave and convex surfaces formed aspherically on both sides.

[0070] With the focal lengths defined in this way for the subgroups G4 and G5, coma (aberration), astigmatism and distortion in the image field are further reduced (minimized).

[0071] To further reduce (minimize) the Petzval sum, it is advantageous if lens L2 of front group VG has a refractive index n of 2.01 (n=2.01), lens L6 of rear group HG has a refractive index n of 2.01 (n=2.01), and lens L1 of front group VG has a refractive index n of 1.49 (n=1.49).

[0072] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.01 (V / Bd 3 = 0.01) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0073] For the embodiment of FIG. 1, the following tables provide the mechanical construction data and optical parameters for each lens element.

[0074] The structural data is the overall focal length f' ges= 1 mm and, in a known manner, for example, for an oval area, the total focal length f' ges = Can be scaled to 24mm.

[0075] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 15 describes the glass-air transition of lens L8, and the aperture stop BL is given as a planar (flat) surface 8.

[0076] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the type of surface. For example, K02 indicates that the second surface is an aspherically curved surface, and H10 indicates that the tenth surface is a diffractive surface. d M indicates the center thickness or the distance to the adjacent surface at the apex of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0077] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0078] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L8, subgroups G1 to G5 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000006.tif93144

[0079] In the following table, the conic constant k and the aspherical coefficients a2 to a6 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H: TIFF0007719181000007.tif78135

[0080] In the compact structure type objective lens shown in Figure 2, the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 1.73 (SO' / Bd=1.73), the half object angle w is 38° (w=38°), and the aperture ratio is F / # 2.0 (F / #=2.0).

[0081] In this objective lens, the small groups G1 to G5 described above are made up of lenses L1 to L8 having the following refractive power arrangement when viewed in the light direction: -+-+++--.

[0082] Given the overall focal length f' of the objective lens ges In contrast, respectively, Focal length f' of the front group VG VG teeth f' VG / f' ges =+19.4 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+2.2 By The focal length of the rear group HG is f' HG teeth f' HG / f' ges =+3.8 It is particularly advantageous to define it as follows:

[0083] The lens L5 of the optical element G3 of the middle group MG, located behind (downstream of) the aperture stop BL, is configured as a convex lens having an aspherical first surface and a planar (flat) second surface when viewed in the direction of light. f' DOE / f' ges =+40.3 Diffractive power f' of DOEThis provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. The planar second surface is particularly suitable for the simple manufacture of diffractive structures, and the aspherical first surface provides compensation of monochromatic aberrations over the entire distance adjustment range.

[0084] The subgroup G1 of the front group VG is composed of two lenses L1 and L2, and as a whole: f' G1 / f' ges =-7.2 The focal length f' G1 It has.

[0085] In this case, the first lens L1 has a convex-concave shape with negative refractive power, and is configured in a meniscus shape with an aspherically curved convex side and an aspherically curved concave side.

[0086] The small group G2 of the front group VG is f' G2 / f' ges =+6.7 The focal length f' G2 It is advantageous to have

[0087] The focal lengths thus defined for the subgroups G1 and G2 ensure compensation of monochromatic aberrations between the image center and the image field.

[0088] The small group G4 of the rear group HG is composed of a biconvex lens L6 and a biconcave lens L7, which are combined to form a f' G4 / f' ges =+3.0 The focal length f' G4 The doublet is configured as

[0089] In one advantageous embodiment, the subgroup G5 of the rear group HG is f' ges / f' G5 =-0.09 The focal length f' G5and is configured as a single lens L8 having an aspherical concave surface and a spherical convex surface.

[0090] With the focal lengths defined in this way for the subgroups G4 and G5, coma (aberration), astigmatism and distortion in the image field are further reduced (minimized).

[0091] To further reduce (minimize) the Petzval sum, it is advantageous if lens L2 of front group VG has a refractive index n of 2.01 (n=2.01), lens L6 of rear group HG has a refractive index n of 2.01 (n=2.01), and lens L1 of front group VG has a refractive index n of 1.49 (n=1.49).

[0092] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.02 (V / Bd 3 = 0.02) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0093] For the embodiment of FIG. 2, the following table gives the mechanical construction data and optical parameters for each lens element.

[0094] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = Can be scaled to 28mm.

[0095] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 15 describes the glass-air transition of lens L8, and the aperture stop BL is given as a planar (flat) surface 8.

[0096] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the type of surface. For example, K01 indicates that the first surface is an aspherically curved surface, and H10 indicates that the tenth surface is a diffractive surface. d M indicates the center thickness or the distance between the adjacent surfaces at the vertices of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0097] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0098] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L8, subgroups G1 to G5 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000008.tif93144

[0099] In the following table, the conic constant k and the aspherical coefficients a2 to a6 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H: TIFF0007719181000009.tif83146

[0100] The objective lens shown in Figure 3 has a compact structure, and the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 1.73 (SO' / Bd=1.73), the half object angle w is 32° (w=32°), and the aperture ratio is F / #2.0 (F / #=2.0).

[0101] In this objective lens, the small groups G1 to G5 described above are made up of lenses L1 to L8 having the following refractive power arrangement when viewed in the light direction: -+-+++--.

[0102] Given the overall focal length f' of the objective lens ges In contrast, respectively, Focal length f' of the front group VG VG teeth f' VG / f' ges =+23.3 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+1.8 By The focal length of the rear group HG is f' HG teeth f' HG / f' ges =+4.5 It is particularly advantageous to define it as follows:

[0103] The lens L5 of the optical element G3 of the middle group MG, located behind (downstream of) the aperture stop BL, is configured as a convex lens having an aspherical first surface and a flat second surface when viewed in the direction of light. f' DOE / f' ges =+40.9 Diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. The planar second surface is particularly suitable for the simple manufacture of diffractive structures, and the aspherical first surface provides compensation of monochromatic aberrations over the entire distance adjustment range.

[0104] The subgroup G1 of the front group VG is composed of two lenses L1 and L2, and as a whole: f' G1 / f' ges =-4.1 The focal length f' G1 It has.

[0105] In this case, the first lens L1 has a convex-concave shape with negative refractive power, and is configured as a meniscus shape having an aspherically curved convex side and a spherically curved concave side.

[0106] The small group G2 of the front group VG is f' G2 / f' ges =+4.2 The focal length f' G2 It is advantageous to have

[0107] The focal lengths thus defined for the subgroups G1 and G2 ensure compensation of monochromatic aberrations between the image center and the image field.

[0108] The small group G4 of the rear group HG is composed of a biconvex lens L6 and a biconcave lens L7, which are combined to form a f' G4 / f' ges =+3.8 The focal length f' G4 The doublet is configured as

[0109] In one advantageous embodiment, the subgroup G5 of the rear group HG is f' G5 / f' ges =-0.04 The focal length f' G5 and is configured as a single lens L8 having aspherical concave and convex surfaces on both sides.

[0110] With the focal lengths defined in this way for the subgroups G4 and G5, coma (aberration), astigmatism and distortion in the image field are further reduced (minimized).

[0111] To further reduce (minimize) the Petzval sum, it is advantageous if lens L2 of front group VG has a refractive index n of 2.06 (n=2.06), lens L6 of rear group HG has a refractive index n of 1.91 (n=1.91), and lens L1 of front group VG has a refractive index n of 1.49 (n=1.49).

[0112] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.02 (V / Bd 3 = 0.02) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0113] For the embodiment of FIG. 3, the following table gives the mechanical construction data and optical parameters for each lens element.

[0114] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = 35mm.

[0115] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 15 describes the glass-air transition of lens L8, and the aperture stop BL is given as a planar (flat) surface 8.

[0116] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the type of surface. For example, K01 indicates that the first surface is an aspherically curved surface, and H10 indicates that the tenth surface is a diffractive surface. d M indicates the center thickness or the distance between the adjacent surfaces at the vertices of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0117] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0118] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L8, subgroups G1 to G5 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000010.tif88136

[0119] In the following table, the conic constant k and the aspherical coefficients a2 to a6 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H: TIFF0007719181000011.tif83144

[0120] The embodiment of the fixed focal length objective shown in FIG. 4 is composed of three optical structures: a front group VG with a positive overall refractive power, a middle group MG with a positive overall refractive power, and a rear group HG with a negative or positive overall refractive power, all of which are located in front of (upstream of) the image position IM as viewed in the light (incident) direction.

[0121] The objective lens has a standardized overall focal length f' ges = 1 mm and in a known manner, for example for an oval area, the overall focal length f' ges = 50mm.

[0122] For normalized representation, the following figures are given as focal length ratios.

[0123] Focal length f' of the front group VG VG teeth +3.4≦f' VG / f' ges ≦+4.9 The focal length of the middle group MG is defined as MG teeth +0.9≦f' MG / f' ges ≦+1.2 and the focal length of the rear group HG is in the range of f' HG teeth -0.0949≦f'ges / f' HG ≦+0.0299 is in the range.

[0124] The front group VG is composed of one subgroup G1, the middle group MG is composed of one optical element G2, and the rear group HG has two subgroups G3 and G4. An aperture stop BL with a variable aperture diameter is located between the first lens L4 and the second lens L5 of the small group G3. By definition, the middle group MG is located in the near-aperture region, i.e., there is only one further optical element, lens L4, between the aperture stop BL and the middle group MG. The middle group MG is composed of one optical element G2 and is supported for movement toward the front group VG in the direction opposite to the optical axis (i.e., in the direction of the arrow) for focusing from the infinity position shown in the figure to the close focus distance.

[0125] In this objective lens, the small groups G1 to G4 described above are made up of lenses L1 to L9 having the following refractive power arrangement when viewed in the light direction: +-+--+-+-.

[0126] Given the overall focal length f' of the objective lens ges In response to the above, Focal length f' of the front group VG VG teeth f' VG / f' ges =+4.4 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+1.0 By The focal length of the rear group HG is f' HG teeth f' ges / f' HG =+0.0271 It is particularly advantageous to define it as follows:

[0127] In one advantageous embodiment, the refractive power f' of the middle group MG MGOn the one hand, it should not be chosen too small (because otherwise the focus stroke from infinity to close-up focusing would be longer), and on the other hand, its refractive power should not be chosen too large (because otherwise the lens volume would increase). If both effects work against each other, the focusing of the objective would become too slow and would no longer be suitable for autofocus use.

[0128] Therefore, in accordance with the present invention, the focal length f' of the middle group MG As already mentioned, f' MG / f' ges =+1.0 should be selected.

[0129] To minimize chromatic aberration (color error) throughout the entire distance adjustment range of the objective lens, the optical element G2 of the middle group MG is +25.5≦f' DOE / f' ges ≦+33.2 Diffractive power f' in the range DOE The lens L3 has the following surface.

[0130] According to the invention, a simple production of the diffractive structures required for the diffractive power is made possible on flat or at most slightly curved surfaces. Thus, in one advantageous embodiment, the apex radius r of the diffractive surface of the lens L3 of the middle group MG is DOE are upper and lower limits -0.1020≦f' MG / r DOE ≦+0.1127 It is flat within the range.

[0131] In one particularly advantageous embodiment, the lens L3 of the optical element G2 of the middle group MG, which is arranged in the close range of the aperture stop BL, is configured as a convex lens having, as viewed in the direction of the light, an aspherical first surface and a planar second surface. f' DOE / f'ges =+27.4 diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. The planar second surface is particularly suitable for the simple manufacture of diffractive structures, and the aspherical first surface provides compensation of monochromatic aberrations over the entire distance adjustment range.

[0132] When adjusting the distance from infinity to a close focus distance, the paraxial imaging magnification β' of the middle group MG MG are upper and lower limits +0.090≦β' MG ≦+0.275 It is advantageous if the temperature is in the range

[0133] +0.103≦β' MG ≦+0.223 In the range of , good correction of aberrations over the entire adjustment range can be achieved.

[0134] The subgroup G1 of the front group VG is composed of two elements L1 and L2, and has a positive refractive power as a whole. G1 teeth f' G1 / f' ges =+4.4 is defined as:

[0135] At least one first lens L1 having a positive refractive power can be configured as a convexo-plano or biconvex lens. In a preferred embodiment, lens L1 is configured as a convexo-concave lens, and its concave side faces the convex side of lens L2, which has a negative refractive power and is configured as a meniscus. In this embodiment, the convex surface of lens L1 is aspherically curved. In this way, correction of monochromatic aberrations at the image center is advantageously achieved.

[0136] The subgroup G3 of the rear group HG includes three elements L4, L5, and L6, each having at least one lens with positive refractive power and at least one lens with negative refractive power, and each having a positive refractive power. The subgroup G3 is advantageously composed of a convex-concave lens L4 with negative refractive power, a biconcave lens L5 with negative refractive power, and a biconvex lens L6 with positive refractive power. L4 is positioned so that its first convex side faces the middle group MG. In this embodiment, elements L5 and L6 are each configured as a single lens, and together they form a doublet.

[0137] The rear group HG's subgroup G4 has a negative overall refractive power and is composed of at least one lens element having a positive refractive power and a final lens element having a negative refractive power and a concave first surface oriented toward the rear group G3. In this embodiment, G4 includes a biconcave lens element L7 that, together with a biconvex lens element L8, forms a doublet. The final lens element L9, which has a negative refractive power and a meniscus shape, is positioned so that its convex surface faces the image position IM.

[0138] Focal length f' of small group G3 G3 teeth f' G3 / f' ges =+3.5 and on the other hand, the focal length f' of the small group G4 G4 teeth f' G4 / f' ges =-4.1 It is advantageous to select

[0139] Due to the characteristics of the subgroups G3 and G4, compensation of monochromatic aberrations can be achieved in an advantageous manner between the image center and the image field.

[0140] Advantageously, the refractive index n of at least one of the lenses having positive refractive power in the front group VG has a value of 1.80 or greater (n≧1.80), with n=1.91 minimizing the Petzval sum.

[0141] More advantageously, the refractive index n of at least one of the lenses having positive refractive power in the rear group HG is selected to be 1.85 or greater (n≧1.85), and with n=1.96 the Petzval sum is further reduced (minimized).

[0142] An Abbe number v of less than or equal to 25 (v≦25), in particular less than or equal to 17 (v≦17), which is advantageously selected for at least one of the lenses with negative refractive power in the front group VG, serves to compensate for chromatic aberrations (color errors).

[0143] It is advantageous if at least one lens in the front group VG is configured aspherically on one or both sides, and if the lens has positive refractive power, the surface facing the object side, and if the lens has negative refractive power, the surface facing the image side, has an aspherical surface.

[0144] In this embodiment, the first surface of the lens L1 in the light direction has an aspherical surface, thus minimizing monochromatic aberrations at the image center.

[0145] A lightweight focusing group MG is advantageous for achieving a high focusing speed. In this case, the ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd on the image plane should be 0.1 or less (V / Bd 3 It has been found to be particularly advantageous if the focusing group has a diameter Bd of 1 / 2 mm or less (≦0.1). In this way, the focusing group is made lighter, allowing for faster focusing. A lighter focusing group also has the advantage of lower power consumption when using autofocus, allowing for quieter focusing. The image circle diameter Bd is also known to those skilled in the art as the image diagonal of the digital imaging sensor Bs and will be explained in more detail using FIG. 10.

[0146] For a compact structure, it is further advantageous if the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 2.0 or less (SO' / Bd≦2.0), where the optical structure length SO' is defined as the distance from the lens vertex of the first lens surface of the lens L1 on the optical axis in the light direction to the image position at the image plane IM.

[0147] An objective lens constructed according to the above-described characteristics advantageously has a half object angle w in the range of 21° to 26° (21°≦w≦26°).

[0148] The objective lens has an aperture ratio F / # of at least 1.7 and at most 2.5 (1.7≦F / #≦2.5).

[0149] The objective lens shown in Figure 4 has an exceptionally compact structure, with a ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM of 1.73 (SO' / Bd=1.73), a half object angle w of 23° (w=23°), and an aperture ratio F / # of 2.0 (F / #=2.0).

[0150] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.02 (V / Bd 3 = 0.02) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0151] For the embodiment of FIG. 4, the following table gives the mechanical construction data and optical parameters for each lens element.

[0152] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = 50mm.

[0153] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 17 describes the glass-air transition of lens L9, and the aperture stop BL is given as a planar (flat) surface 9.

[0154] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the type of surface. For example, K01 indicates that the first surface is an aspherically curved surface, and H06 indicates that the sixth surface is a diffractive surface. d M indicates the center thickness or the distance between the adjacent surfaces at the vertices of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0155] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0156] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L9, subgroups G1 to G4 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000012.tif99137

[0157] In the following table, the conic constant k and the aspherical coefficients a2 to a6 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H06: TIFF0007719181000013.tif62144

[0158] The embodiment of the fixed focal length objective shown in FIG. 5 is composed of three optical structures: a front group VG with a positive overall refractive power, a middle group MG with a positive overall refractive power, and a rear group HG with a negative or positive overall refractive power, all of which are located in front of (upstream of) the image position IM as viewed in the light (incident) direction.

[0159] The objective lens has a standardized overall focal length f' ges = 1 mm and in a known manner, for example for an oval area, the overall focal length f' ges = 50mm.

[0160] For normalized representation, the following figures are given as focal length ratios.

[0161] Focal length f' of the front group VG VG teeth +3.4≦f' VG / f' ges ≦+4.9 The focal length of the middle group MG is defined as MG teeth +0.9≦f' MG / f' ges ≦+1.2 and the focal length of the rear group HG is in the range of f' HG teeth -0.0949≦f' ges / f' HG ≦+0.0299 is in the range.

[0162] The front group VG is composed of one subgroup G1, the middle group MG is composed of one optical element G2, and the rear group HG has two subgroups G3 and G4. An aperture stop BL with a variable aperture diameter is located in front of (upstream of) the first lens element L4 of the subgroup G3. By definition, the middle group MG is located in the near-aperture region in front of the aperture stop BL as viewed in the direction of light. The middle group MG is composed of one optical element G2 and is supported so as to be movable toward the front group VG in the direction opposite to the direction of light (i.e., in the direction of the arrow shown in the figure) for focusing from the infinity position shown in the figure to the close focus distance.

[0163] In this objective lens, the small groups G1 to G4 described above are made up of lenses L1 to L7 having the following refractive power arrangement when viewed in the light direction: +-+-++-.

[0164] Given the overall focal length f' of the objective lens ges In contrast, respectively, Focal length f' of the front group VG VG teeth f' VG / f' ges =+3.8 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+1.1 By The focal length of the rear group HG is f' HG teeth f' ges / f' HG =-0.0858 It is particularly advantageous to define it as follows:

[0165] In one advantageous embodiment, the refractive power f' of the middle group MG MG On the one hand, it should not be chosen too small (because otherwise the focus stroke from infinity to close-up focusing would be longer), and on the other hand, its refractive power should not be chosen too large (because otherwise the lens volume would increase). If both effects work against each other, the focusing of the objective would become too slow and would no longer be suitable for autofocus use.

[0166] Therefore, in accordance with the present invention, the focal length f' of the middle group MG As already mentioned, f' MG / f' ges =+1.1 should be selected.

[0167] To minimize chromatic aberration (color error) throughout the entire distance adjustment range of the objective lens, the optical element G2 of the middle group MG is +25.5≦f' DOE / f' ges ≦+33.2 Diffractive power f' in the range DOE The lens L3 has the following surface.

[0168] According to the invention, the simple manufacture of the diffractive structures required for the diffractive power is made possible on flat or at most slightly curved surfaces. Thus, in one advantageous embodiment, the vertex radius r of the diffractive surface of the lens L3 of the middle group MG is DOE are upper and lower limits -0.1020≦f' MG / r DOE ≦+0.1127 It is flat within the range.

[0169] In one particularly advantageous embodiment, the lens L3 of the optical element G2 of the middle group MG, which is arranged in the close range of the aperture stop BL, is configured as a convex lens having, as viewed in the direction of the light, an aspherical first surface and a planar second surface. f' DOE / f' ges =+29.2 Diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. The planar second surface is particularly suitable for the simple manufacture of diffractive structures, and the aspherical first surface provides compensation of monochromatic aberrations over the entire distance adjustment range.

[0170] When adjusting the distance from infinity to a close focus distance, the paraxial imaging magnification β' of the middle group MG MG are upper and lower limits +0.090≦β' MG ≦+0.275 It is advantageous if the temperature is in the range

[0171] +0.139≦β' MG ≦+0.254 In the range of , good correction of aberrations over the entire adjustment range can be achieved.

[0172] The subgroup G1 of the front group VG is composed of two elements L1 and L2, and has a positive refractive power as a whole. G1 teeth f' G1 / f' ges =+3.8 is defined as:

[0173] At least one first lens L1 having a positive refractive power can be configured as a convexo-plano or biconvex lens. In a preferred embodiment, lens L1 is configured as a convexo-concave lens, and its concave side faces the convex side of lens L2, which has a negative refractive power and is configured as a meniscus. In this embodiment, the convex surface of lens L1 is aspherically curved. In this way, correction of monochromatic aberrations at the image center is advantageously achieved.

[0174] The subgroup G3 of the rear group HG includes two elements L4 and L5, each having at least one lens with positive refractive power and at least one lens with negative refractive power, and each having a positive refractive power. Advantageously, the subgroup G3 is composed of a biconcave lens L4 with negative refractive power and a biconvex lens L5 with positive refractive power. In this embodiment, elements L4 and L5 are each configured as a single lens.

[0175] The rear group HG has a negative overall refractive power and is composed of at least one lens element having a positive refractive power and a final lens element having a negative refractive power and a concave first surface oriented toward the rear group HG. In this embodiment, G4 is composed of a concave-convex lens element L6 and a final lens element L7 having a negative refractive power, a meniscus shape, and an orientation in which the convex surface faces the image position IM.

[0176] Focal length f' of small group G3 G3 teeth f' G3 / f' ges =+4.1 and on the other hand, the focal length f' of the small group G4G4 teeth f' G4 / f' ges =-3.21 It is advantageous to select

[0177] Due to the characteristics of the subgroups G3 and G4, compensation of monochromatic aberrations can be achieved in an advantageous manner between the image center and the image field.

[0178] Advantageously, the refractive index n of at least one of the lenses having positive refractive power in the front group VG has a value of 1.80 or greater (n≧1.80), with n=1.96 minimizing the Petzval sum.

[0179] More preferably, the refractive index n of at least one of the lenses having positive refractive power in the rear group HG is selected to be 1.85 or greater (n≧1.85), and with n=1.89 the Petzval sum is further reduced (minimized).

[0180] An Abbe number v of less than or equal to 25 (v≦25), in particular less than or equal to 23 (v≦23), which is advantageously selected for at least one of the lenses with negative refractive power in the front group VG, serves to compensate for chromatic aberrations (color errors).

[0181] It is advantageous if at least one lens in the front group VG is configured aspherically on one or both sides, and if the lens has positive refractive power, the surface facing the object side, and if the lens has negative refractive power, the surface facing the image side, has an aspherical surface.

[0182] In this embodiment, the first surface of the lens L1 in the light direction has an aspherically formed surface, thus minimizing monochromatic aberrations at the image center.

[0183] For compensation of monochromatic aberrations in the image field, the last lens of the rear group HG is advantageously formed with an aspherical surface on one or both sides.

[0184] In this embodiment, the first lens surface of the lens L7, which is formed concavely in the light direction, has an aspherical shape.

[0185] A lightweight focusing group MG is advantageous for achieving a high focusing speed. In this case, the ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd on the image plane should be 0.1 or less (V / Bd 3 It has been found to be particularly advantageous if the focusing group has a diameter Bd of 1 / 2 mm or less (≦0.1). In this way, the focusing group is made lighter, allowing for faster focusing. A lighter focusing group also has the advantage of lower power consumption when using autofocus, allowing for quieter focusing. The image circle diameter Bd is also known to those skilled in the art as the image diagonal of the digital imaging sensor Bs and will be explained in more detail below with reference to FIG. 10.

[0186] For a compact structure, it is further advantageous if the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 2.0 or less (SO' / Bd≦2.0), where the optical structure length SO' is defined as the distance from the vertex of the first lens surface of the lens L1 on the optical axis in the light direction to the image position IM.

[0187] An objective lens constructed according to the above-described characteristics advantageously has a half object angle w in the range of 21° to 26° (21°≦w≦26°).

[0188] The objective lens has an aperture ratio F / # of at least 1.7 and at most 2.5 (1.7≦F / #≦2.5).

[0189] The objective lens shown in Figure 5 has an exceptionally compact structure, with a ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM of 1.73 (SO' / Bd=1.73), a half object angle w of 23° (w=23°), and an aperture ratio F / # of 2.0 (F / #=2.0).

[0190] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.01 (V / Bd 3 = 0.01) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0191] For the embodiment of FIG. 5, the following table gives the mechanical construction data and optical parameters for each lens element.

[0192] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = 50mm.

[0193] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 15 describes the glass-air transition of lens L7, and the aperture stop BL is given as a planar (flat) surface 7.

[0194] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the type of surface. For example, K01 indicates that the first surface is an aspherically curved surface, and H06 indicates that the sixth surface is a diffractive surface. d M indicates the center thickness or the distance to the adjacent surface at the apex of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0195] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0196] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L7, subgroups G1 to G4 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000014.tif93147

[0197] In the following table, the conic constant k and the aspherical coefficients a2 to a7 are given for the aspherical surfaces designated by the letter K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated by the letter H06: TIFF0007719181000015.tif73144

[0198] The embodiment of the fixed focal length objective lens shown in FIG. 6 is composed of three optical structures: a front group VG having a positive overall refractive power, a middle group MG having a positive overall refractive power, and a rear group HG having a positive overall refractive power, all of which are located in front of (upstream of) the image position IM when viewed in the light (incident) direction.

[0199] The objective lens has a standardized overall focal length f' ges = 1 mm and in a known manner, for example for an oval area, the overall focal length f' ges = 75mm.

[0200] For normalized representation, the following figures are given as focal length ratios.

[0201] Focal length f' of the front group VG VG teeth +1.4≦f' VG / f' ges ≦+2.2 The focal length of the middle group MG is defined as MG teeth +0.5≦f' MG / f' ges ≦+1.0 and the positive or negative focal length f' of the rear group HG is in the range HG teeth 2.3≦|f' HG / f'ges |≦+3.8 The absolute value of is in the range of .

[0202] The front group VG is composed of three lens elements L1, L2, and L3, the middle group MG is composed of one optical element L4, and the rear group HG has two sub-groups G3 and G4. An aperture stop BL with a variable aperture diameter is located between the middle group MG and the rear group HG. By definition, the middle group MG is located in the near-aperture region, i.e., there is at most one optical element between the aperture stop BL and the middle group MG, but in this embodiment, no additional optical elements are located. The middle group MG is supported so that it can move toward the front group VG in the direction opposite to the optical axis (i.e., in the direction of the arrow) for focusing from the infinity position shown in the figure to the close focus distance.

[0203] In this objective lens, the above-mentioned groups VG, MG, and HG are each made up of lenses L1 to L9 having the following refractive power arrangement when viewed in the light direction: ++-+-+-+-.

[0204] Given the overall focal length f' of the objective lens ges In contrast, respectively, Focal length f' of the front group VG VG teeth f' VG / f' ges =+2.0 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+0.9 By Positive or negative focal length f' of rear group HG HG teeth |f' HG / f' ges |=3.4 It is particularly advantageous to define it as follows:

[0205] In one advantageous embodiment, the refractive power f' of the middle group MG MGOn the one hand, it should not be chosen too small (because otherwise the focus stroke from infinity to close-up focusing would be longer), and on the other hand, its refractive power should not be chosen too large (because otherwise the lens volume would increase). If both effects work against each other, the focusing of the objective would become too slow and would no longer be suitable for autofocus use.

[0206] Therefore, in accordance with the present invention, the focal length f' of the middle group MG As already mentioned, f' MG / f' ges =+0.9 should be selected.

[0207] To minimize chromatic aberration (color error) throughout the entire distance adjustment range of the objective lens, the optical elements in the middle group MG are +14.9≦f' DOE / f' ges ≦+24.9 Diffractive power f' in the range DOE The lens L4 has the following surface.

[0208] According to the invention, a simple production of the diffractive structures required for the diffractive power is made possible on a flat or at most slightly curved surface. Advantageously, therefore, in this embodiment, the focal length f' MG The apex radius r of the diffractive surface of the lens L4 in the middle group MG is DOE teeth, f' MG / r DOE =0.2849 Or r DOE ≧3.159mm is defined as being substantially planar (nearly flat) for purposes of the present invention.

[0209] In one particularly advantageous embodiment, the lens L4 of the middle group MG, which is located in the close range of the aperture stop BL, is configured as a convex lens having a positive refractive power and having an aspherical first surface and a substantially planar second surface when viewed in the direction of the light. f' DOE / f' ges =+22.5 Diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. The substantially planar second surface is particularly suitable for the simple manufacture of diffractive structures, and the aspherical first surface provides compensation for monochromatic aberrations over the entire distance adjustment range.

[0210] When adjusting the distance from infinity to a close focus distance, the paraxial imaging magnification β' of the middle group MG MG are upper and lower limits +0.254≦β' MG ≦+0.415 It is advantageous if the temperature is in the range

[0211] +0.266≦β' MG ≦+0.396 In the range of , good correction of aberrations over the entire adjustment range can be achieved.

[0212] The front group VG is composed of at least one first lens L1 having positive refractive power, and a final lens having a first concave side (foremost) in the light direction and negative refractive power.

[0213] In this embodiment, the front group VG is formed of three lenses L1, L2, and L3, and has a positive refractive power as a whole. Lenses L1 and L2 are configured as convex-concave or convex-plano lenses with positive refractive power, and lens L3 is configured as a meniscus-shaped convex-concave lens with negative refractive power. In this way, correction of monochromatic aberrations at the image center is advantageously achieved.

[0214] The subgroup G3 of the rear group HG has negative refractive power and is composed of at least one first lens element having negative refractive power and a final lens element having positive refractive power. In this embodiment, subgroup G3 is composed of lens elements L5 and L6. In one advantageous embodiment, lens L5 is configured as a plano-concave lens having negative refractive power with a flat surface oriented toward the aperture stop BL or the middle group MG, while lens L6 is configured as a biconvex lens having positive refractive power.

[0215] The subgroup G4 of the rear group HG has a positive overall refractive power and includes at least one penultimate lens (one lens before the final lens) having positive refractive power, and a final lens having negative refractive power and a first surface thereof concavely oriented toward the subgroup G3. In this embodiment, the subgroup G4 includes a biconcave lens L7 having negative refractive power, a biconvex lens L8 having positive refractive power, and a final lens L9 having negative refractive power, a meniscus shape, and an orientation in which its convex surface faces the image position IM.

[0216] Focal length f' of small group G3 G3 teeth f' G3 / f' ges =-2.8 and on the other hand, the focal length f' of the small group G4 G4 teeth f' G4 / f' ges =+9.7 It is advantageous to select

[0217] Due to the characteristics of the subgroups G3 and G4, compensation of monochromatic aberrations can be achieved in an advantageous manner between the image center and the image field.

[0218] Advantageously, the refractive index n of at least one of the lenses having positive refractive power in the front group VG has a value greater than or equal to 1.85 (n≧1.85), with n=1.92 minimizing the Petzval sum.

[0219] An Abbe number v of 60 or greater (v≧60), in particular 71 (v=71), which is advantageously selected for at least one of the lenses with positive refractive power in the front group VG, serves to compensate for or minimize chromatic aberrations (color errors).

[0220] More preferably, the refractive index n of at least one of the lenses having negative refractive power in the front group VG is selected to be less than or equal to 1.75 (n≦1.75), with n=1.70 to minimize the Petzval sum.

[0221] The last lens of the rear group HG is advantageously aspherically configured on one or both sides. In this embodiment, the last lens L9 is aspherically configured on one side, and the first surface of lens L9, which is concave in the light direction, has an aspherically configured surface. In this way, monochromatic aberrations at the image center are minimized.

[0222] A lightweight focusing group MG is advantageous for high focusing speed. In this case, the ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd on the image plane should be less than 0.1 (V / Bd 3 <0.1) has proven to be particularly advantageous. In this way, the focusing group is made lighter, allowing for faster focusing. A lighter focusing group also has the advantage of lower power consumption when using autofocus, allowing for quieter focusing. The image circle diameter Bd is also known to those skilled in the art as the image diagonal of the digital imaging sensor Bs and will be explained in more detail below with reference to FIG. 10.

[0223] For a compact structure, it is further advantageous if the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 3.0 or less (SO' / Bd≦3.0), where the optical structure length SO' is defined as the distance from the lens vertex of the first lens surface of the lens L1 on the optical axis in the light direction to the image position IM at the image plane.

[0224] An objective lens constructed according to the above-described characteristics advantageously has a half object angle w in the range of 10° to 18° (10°≦w≦18°).

[0225] The objective lens has an aperture ratio F / # of at least 1.7 and at most 2.5 (1.7≦F / #≦2.5).

[0226] The objective lens shown in Figure 6 has an exceptionally compact structure, with a ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM of 2.08 (SO' / Bd=2.08), a half object angle w of 16° (w=16°), and an aperture ratio F / # of 2.0 (F / #=2.0).

[0227] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.02 (V / Bd 3 = 0.02) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0228] For the embodiment of FIG. 6, the following table gives the mechanical construction data and optical parameters for each lens element.

[0229] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = 75mm.

[0230] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 19 describes the glass-air transition of lens L9, and the aperture stop BL is given as a planar (flat) surface 9.

[0231] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the surface type. For example, K07 indicates that surface 7 is an aspherically curved surface, and H08 indicates that surface 8 is a diffractive surface. d M indicates the center thickness or the distance between the adjacent surfaces at the vertices of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0232] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0233] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L9, subgroups G1 to G4 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000016.tif109140

[0234] In the following table, the conic constant k and the aspherical coefficients a2 to a6 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H08: TIFF0007719181000017.tif62148

[0235] The embodiment of the fixed focal length objective lens shown in Figure 7 is composed of three optical structures: a front group VG with positive overall refractive power, a middle group MG with positive overall refractive power, and a rear group HG with positive overall refractive power, all of which are located in front of (upstream of) the image position IM when viewed in the light (incident) direction.

[0236] The objective lens has a standardized overall focal length f' ges = 1 mm and in a known manner, for example for an oval area, the overall focal length f'ges = 100 mm.

[0237] For normalized representation, the following figures are given as focal length ratios.

[0238] Focal length f' of the front group VG VG teeth +1.4≦f' VG / f' ges ≦+2.2 The focal length of the middle group MG is defined as MG teeth +0.5≦f' MG / f' ges ≦+1.0 and the positive or negative focal length f' of the rear group HG is in the range HG teeth +2.3≦|f' HG / f' ges |≦+3.8 The absolute value of is in the range of .

[0239] The front group VG is composed of three lens elements L1, L2, and L3, the middle group MG is composed of one optical element L4, and the rear group HG has two sub-groups G3 and G4. An aperture stop BL with a variable aperture diameter is located between the middle group MG and the rear group HG. By definition, the middle group MG is located in the near-aperture region, i.e., there is at most one optical element between the aperture stop BL and the middle group MG, but in this embodiment, no additional optical elements are located. The middle group MG is supported so that it can move toward the front group VG in the direction opposite to the optical axis (i.e., in the direction of the arrow) for focusing from the infinity position shown in the figure to the close focus distance.

[0240] In this objective lens, the above-mentioned groups VG, MG, and HG are each made up of lenses L1 to L10 having the following refractive power arrangement when viewed in the light direction: ++-+--+-+-.

[0241] Given the overall focal length f' of the objective lens ges In contrast, respectively, Focal length f' of the front group VG VGteeth f' VG / f' ges =+1.5 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+0.6 By Positive or negative focal length f' of rear group HG HG teeth |f' HG / f' ges |=+2.5 It is particularly advantageous to define it as follows:

[0242] In one advantageous embodiment, the refractive power f' of the middle group MG MG On the one hand, it should not be chosen too small (because otherwise the focus stroke from infinity to close-up focusing would be longer), and on the other hand, its refractive power should not be chosen too large (because otherwise the lens volume would increase). If both effects work against each other, the focusing of the objective would become too slow and would no longer be suitable for autofocus use.

[0243] Therefore, in accordance with the present invention, the focal length f' of the middle group MG MG As already mentioned, f' MG / f' ges =+0.6 should be selected.

[0244] To minimize chromatic aberration (color error) throughout the entire distance adjustment range of the objective lens, the optical elements in the middle group MG are +14.9≦f' DOE / f' ges ≦+24.9 Diffractive power f' in the range DOE The lens L4 has the following surface.

[0245] According to the invention, a simple production of the diffractive structures required for the diffractive power is made possible on a flat or at most slightly curved surface. Thus, in this embodiment, advantageously, the focal length f' MG The apex radius r of the diffractive surface of the lens L4 in the middle group MG is DOE teeth, f' MG / r DOE =0.5923 Or r DOE ≧1.013mm is defined as being substantially planar (nearly flat) for purposes of the present invention.

[0246] In one particularly advantageous embodiment, the lens L4 of the middle group MG, located in the close range of the aperture stop BL, is configured as a convex lens having a positive refractive power and having an aspherical first surface and a substantially planar second surface when viewed in the direction of the light. f' DOE / f' ges =+16.7 Diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. The substantially planar second surface is particularly suitable for the simple manufacture of diffractive structures, and the aspherical first surface provides compensation for monochromatic aberrations over the entire distance adjustment range.

[0247] When adjusting the distance from infinity to a close focus distance, the paraxial imaging magnification β' of the middle group MG MG are upper and lower limits +0.254≦β' MG ≦+0.415 It is advantageous if the temperature is in the range

[0248] +0.281≦β' MG ≦+0.395 In the range of , good correction of aberrations over the entire adjustment range can be achieved.

[0249] The front group VG is composed of at least one first lens L1 having positive refractive power, and a final lens having a first concave side in the light direction and negative refractive power.

[0250] In this embodiment, the front group VG is formed of three lenses L1, L2, and L3, and has a positive refractive power as a whole. Lenses L1 and L2 can be configured as plano-convex or biconvex lenses. In this embodiment, they are configured as convex-concave lenses with positive refractive power, and lens L3 is configured as a meniscus-shaped convex-concave lens with negative refractive power. In this way, correction of monochromatic aberrations at the image center is advantageously achieved.

[0251] The subgroup G3 of the rear group HG has negative refractive power and is composed of at least one first lens element having negative refractive power and a final lens element having positive or negative refractive power. In this embodiment, the subgroup G3 is composed of lens elements L5, L6, and L7. In one advantageous embodiment, the lens L5 is configured as a biconcave lens having negative refractive power. The lens L6 is configured as a biconcave lens having negative refractive power and is configured as a lens doublet with the lens L7, which is a biconvex lens having positive refractive power.

[0252] The subgroup G4 of the rear group HG has a positive overall refractive power and is composed of at least one penultimate lens (one lens before the final lens) having positive refractive power and a final lens having negative refractive power and a first surface thereof oriented concavely toward the subgroup G3. In this embodiment, the subgroup G4 is composed of a meniscus-shaped convex-concave lens L8 having negative refractive power, a biconvex lens L9 having positive refractive power, and a meniscus-shaped concave-convex lens L10 having negative refractive power, which together form a lens triplet.

[0253] Focal length f' of small group G3 G3 teeth f' G3 / f' ges =-0.5 and on the other hand, the focal length f' of the small group G4 G4 teeth f' G4 / f' ges =+0.5 It is advantageous to select

[0254] Due to the characteristics of the subgroups G3 and G4, compensation of monochromatic aberrations can be achieved in an advantageous manner between the image center and the image field.

[0255] Advantageously, the refractive index n of at least one of the lenses having positive refractive power in the front group VG has a value of 1.85 or greater (n≧1.85), with n=1.96 minimizing the Petzval sum.

[0256] An Abbe number v of 60 or greater (v≧60), in particular 68 (v=68), which is advantageously selected for at least one of the lenses with positive refractive power in the front group VG, serves to compensate for or minimize chromatic aberrations (color errors).

[0257] More preferably, the refractive index n of at least one of the lenses having negative refractive power in the front group VG is selected to be less than or equal to 1.75 (n≦1.75), with n=1.73 to minimize the Petzval sum.

[0258] A lightweight focusing group MG is advantageous for high focusing speed. In this case, the ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd on the image plane should be less than 0.1 (V / Bd 3 <0.1) has proven to be particularly advantageous. In this way, the focusing group is made lighter, allowing for faster focusing. A lighter focusing group also has the advantage of lower power consumption when using autofocus, allowing for quieter focusing. The image circle diameter Bd is also known to those skilled in the art as the image diagonal of the digital imaging sensor Bs and will be explained in more detail below with reference to FIG. 10.

[0259] For a compact structure, it is further advantageous if the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 3.0 or less (SO' / Bd≦3.0), where the optical structure length SO' is defined as the distance from the lens vertex of the first lens surface of the lens L1 on the optical axis in the light direction to the image position IM at the image plane.

[0260] An objective lens constructed according to the above-described characteristics advantageously has a half object angle w in the range of 10° to 18° (10°≦w≦18°).

[0261] The objective lens has an aperture ratio F / # of at least 1.7 and at most 2.5 (1.7≦F / #≦2.5).

[0262] The objective lens shown in Figure 7 has an exceptionally compact structure, with the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM being 2.77 (SO' / Bd=2.77), the half object angle w being 12° (w=12°), and the aperture ratio F / # being 2.0 (F / #=2.0).

[0263] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.02 (V / Bd 3 = 0.02) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0264] For the embodiment of FIG. 7, the following table gives the mechanical construction data and optical parameters for each lens element.

[0265] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = 100 mm.

[0266] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 18 describes the glass-air transition of lens L10, and the aperture stop BL is given as a planar (flat) surface 9.

[0267] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the surface type. For example, K07 indicates that surface 7 is an aspherically curved surface, and H08 indicates that surface 8 is a diffractive surface. d M indicates the center thickness or the distance to the adjacent surface at the apex of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0268] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0269] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L10, subgroups G1 to G4 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000018.tif109147

[0270] In the following table, the conic constant k and the aspherical coefficients a2 to a4 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H08: TIFF0007719181000019.tif31146

[0271] The fixed focal length objective lens embodiment shown in Figures 8 and 9 is composed of three optical structures: a front group VG, a middle group MG, and a rear group HG, each of which has a positive overall refractive power and is located in front of (upstream of) the image position IM as viewed in the light (incident) direction.

[0272] The objective lens has a standardized overall focal length f' ges = 1 mm and in a known manner, for example for an oval area, the overall focal length f' ges = Can be scaled to 28mm.

[0273] For normalized representation, the following figures are given as focal length ratios.

[0274] Focal length f' of the front group VG VG teeth +7.0≦f' VG / f' ges ≦+25.7 The focal length of the middle group MG is defined as MG teeth +1.6≦f' MG / f' ges ≦+3.0 and the focal length of the rear group HG is in the range of f' HG teeth +3.1≦f' HG / f' ges ≦+5.0 is in the range.

[0275] The front group VG is composed of two subgroups G1 and G2, the middle group MG is composed of one optical element [subgroup] G3, and the rear group HG has two subgroups G4 and G5. Between the front group VG and the middle group MG is an aperture stop BL with a variable aperture diameter. By definition, the middle group MG is located in the near-aperture region, i.e., no further optical elements are provided between the aperture stop BL and the middle group MG. The middle group MG is composed of one optical subgroup G3 and is supported for movement toward the aperture stop BL in the direction opposite to the optical axis (i.e., in the direction of the arrow shown) for focusing from the infinity position shown in the figure to the close focus distance.

[0276] In one advantageous embodiment, the refractive power f' of the middle group MG MG On the one hand, it should not be chosen too small (because otherwise the focus stroke from infinity to close-up focusing would be longer), and on the other hand, its refractive power should not be chosen too large (because otherwise the lens volume would increase). If both effects work against each other, the focusing of the objective would become too slow and would no longer be suitable for autofocus use.

[0277] Therefore, in accordance with the present invention, the focal length f' of the middle group MG MG teeth, +1.6≦f' MG / f' ges ≦+3.0 should be selected.

[0278] In order to minimize chromatic aberration (color error) over the entire distance adjustment range of the objective lens, the optical element G3 of the middle group MG is composed of a lens L5 having a positive refractive power and a lens L6 having a positive refractive power. +33.6≦f' DOE / f' ges ≦+45.4 Power f' in the range DOE and configured as a lens L6 having a diffractive surface on one side.

[0279] According to the invention, the simple manufacture of the diffractive structure required for the diffractive power is made possible on a flat or at most slightly curved surface of one of the lenses of the middle group MG. Advantageously, therefore, the apex radius r of the diffractive surface of this lens of the middle group MG is DOE are the upper and lower limits -0.1255≦f' MG / r DOE ≦+0.1388 It is flat within the range.

[0280] If the surfaces of the lenses of the middle group MG directed towards the aperture stop BL have a positive refractive power and are preferably aspherically designed, compensation of monochromatic aberrations over the distance adjustment range is ensured in an advantageous manner.

[0281] The subgroup G1 of the front group VG is composed of two elements L1 and L2, and has a negative refractive power as a whole. G1 is the range f' G1 / f' ges ≦-3.7 is defined by

[0282] At least one first convex / concave lens L1 having negative refractive power is configured in a meniscus shape and is arranged so that its concave side faces the convex side of at least one lens L2 having positive refractive power.

[0283] The subgroup G2 of the front group VG has two elements L3 and L4, which have a positive refractive power as a whole. At least one first lens L3 with negative refractive power is biconcave and is arranged with its first concave side directed toward the lens L2 of the subgroup G1. The second element of the subgroup G2 has at least one lens L4 with positive refractive power. In this embodiment, elements L3 and L4 are configured as single lenses, and together they form a doublet.

[0284] Due to the characteristics of the subgroups G1 and G2, compensation of monochromatic aberrations is advantageously effected between the image center and the image field.

[0285] The subgroup G4 of the rear group HG has two elements L7 and L8 and has a positive refractive power as a whole. The subgroup G4 has at least one biconvex lens L7 with positive refractive power and at least one biconcave lens L8 with negative refractive power. L7 is positioned so that its first convex side is directed toward the middle group MG. In this embodiment, elements L7 and L8 are configured as single lenses, and together they form a doublet.

[0286] The subgroup G5 of the rear group HG has a negative or positive overall refractive power and is composed of at least one final lens L9, the first surface of which is concave and is arranged to be directed toward the subgroup G4. In this case, the focal length f' of the subgroup G5 is G5 is the range -0.1≦f' ges / f' G5 ≦+0.1 is defined by

[0287] The characteristics of the subgroups G4 and G5 make it possible to advantageously achieve a minimization of coma (aberration), astigmatism and distortion in the image field.

[0288] Advantageously, the refractive index n of at least one of the lenses having positive refractive power in the front group VG has a value of 1.85 or greater (n≧1.85), and in this way the Petzval sum is minimized.

[0289] More advantageously, in order to further minimize (reduce) the Petzval sum, the refractive index n of at least one of the lenses having positive refractive power in the rear group HG is also selected to be 1.85 or greater (n≧1.85).

[0290] An advantageously selected refractive index n of the first lens element having a negative refractive power of the front group VG of less than or equal to 1.60 (n≦1.60) also contributes to minimizing the Petzval sum.

[0291] To compensate for monochromatic aberrations in the image field, the first lens L1 of the front group VG is constructed with one or both aspherical surfaces.

[0292] Advantageously, the last lens L9 of the rear group HG is constructed with aspherical surfaces on one or both sides in order to achieve further compensation of monochromatic aberrations in the image field.

[0293] A lightweight focusing group MG is advantageous for high focusing speed. In this case, the ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd on the image plane should be less than 0.1 (V / Bd 3 <0.1) has proven to be particularly advantageous. In this way, the focusing group is made lighter, allowing for faster focusing. A lighter focusing group also has the advantage of lower power consumption when using autofocus, allowing for quieter focusing. The image circle diameter Bd is also known to those skilled in the art as the image diagonal of the digital imaging sensor Bs and will be explained in more detail below with reference to FIG. 10.

[0294] For a compact structure, it is further advantageous if the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 2.0 or less (SO' / Bd≦2.0), where the optical structure length SO' is defined as the distance from the lens vertex of the first lens surface of the lens L1 on the optical axis in the light direction to the image position IM at the image plane.

[0295] Advantageously, an objective lens constructed according to the above-described characteristics has a half object angle w of 31° or greater (w≧31°).

[0296] The objective lens has an aperture ratio F / # of at least 1.7 and at most 2.5, advantageously in the range 1.7 to 2.5 (1.7≦F / #≦2.5).

[0297] The objective lens shown in Figure 8 has a compact structure, and the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 1.73 (SO' / Bd=1.73), the half object angle w is 42° (w=42°), and the aperture ratio F / # is 2.0 (F / #=2.0).

[0298] In this objective, the aforementioned subgroups G1 to G5 are composed of lenses L1 to L9 having the following refractive power sequence in the light (incident) direction: -+-++0+-- (0 means neutral, flat, no refractive power).

[0299] Given the overall focal length f' of the objective lens ges In response to the above, Focal length f' of the front group VG VG teeth f' VG / f' ges =+8.7 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+2.6 By The focal length of the rear group HG is f' HG teeth f' HG / f' ges =+3.5 It is particularly advantageous to define it as follows:

[0300] The lens L5 of the optical element G3 of the middle group MG, located behind (downstream of) the aperture stop BL, is configured as a convex lens having an aspherical first surface when viewed in the direction of the light, and the second surface can be configured as a flat or concave surface.

[0301] The lens L6, which in this embodiment is configured as an optically transparent plate, has, on its side directed towards the image position IM: f' DOE / f' ges =+36.5 diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. An optically transparent plate is particularly suitable for the simple manufacture of diffractive structures. The aspherical first surface of lens L5 provides compensation for monochromatic aberrations over the distance adjustment range.

[0302] The subgroup G1 of the front group VG is composed of two lenses L1 and L2, and as a whole: f' G1 / f' ges =-10.0 The focal length f' G1 It has.

[0303] In this case, the first lens L1 has a convex-concave shape with negative refractive power, and is configured in a meniscus shape with an aspherically curved convex side and an aspherically curved concave side.

[0304] The small group G2 of the front group VG is f' G2 / f' ges =+5.6 The focal length f' G2 It is advantageous to have

[0305] The focal lengths thus defined for the subgroups G1 and G2 ensure compensation of monochromatic aberrations between the image center and the image field.

[0306] The small group G4 of the rear group HG is composed of a biconvex lens L7 and a biconcave lens L8, which are combined to form a f' G4 / f' ges =+2.9 The focal length f' G4 The doublet is configured as

[0307] In one advantageous embodiment, the subgroup G5 of the rear group HG is f' G5 / f' ges =+0.056 The focal length f' G5 The first concave side of the lens L9 in the light direction is configured to be aspherical.

[0308] With the focal lengths defined in this way for the subgroups G4 and G5, coma (aberration), astigmatism and distortion in the image field are further reduced (minimized).

[0309] Advantageously, lens L2 of the front group VG and lens L7 of the rear group HG have the same refractive index. This configuration provides for using the same glass material for both lenses, which in this way facilitates manufacturing and reduces storage costs. To further minimize the Petzval sum, it is particularly advantageous for L2 and L7 to have a refractive index of 2.01 (n=2.01) and for lens L1 of the front group VG to have a refractive index of 1.49 (n=1.49).

[0310] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.04 (V / Bd 3 = 0.04) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0311] For the embodiment of FIG. 8, the following table provides the mechanical construction data and optical parameters for each lens element.

[0312] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = Can be scaled to 28mm.

[0313] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 17 describes the glass-air transition of lens L9, and the aperture stop BL is given as a planar (flat) surface 8.

[0314] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the type of surface. For example, K01 indicates that the first surface is an aspherically curved surface, and H12 indicates that the twelfth surface is a diffractive surface. d Mindicates the center thickness or the distance between the adjacent surfaces at the vertices of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0315] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0316] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L9, subgroups G1 to G5 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000020.tif99147

[0317] In the following table, the conic constant k and the aspherical coefficients a2 to a6 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H12: TIFF0007719181000021.tif83154

[0318] The objective lens shown in Figure 9 has a compact structure, and the ratio of the optical structure length SO' of the objective lens to the image circle diameter Bd at the image plane IM is 1.73 (SO' / Bd = 1.73), the half object angle w is 42° (w = 42°), and the aperture ratio F / # is 2.0 (F / # = 2.0).

[0319] In this objective lens, the small groups G1 to G5 described above are made up of lenses L1 to L9 having the following refractive power arrangement when viewed in the light (incident) direction: -+-++++--.

[0320] Given the overall focal length f' of the objective lens ges In response to the above, Focal length f' of the front group VG VG teeth f' VG / f' ges =+7.5 By Focal length f' of middle group MG MG teeth f' MG / f' ges =+2.8 By The focal length of the rear group HG is f' HG teeth f' HG / f' ges =+3.0 It is particularly advantageous to define it as follows:

[0321] The lens L5 of the optical element G3 of the middle group MG, which is arranged behind (downstream of) the aperture stop BL, is configured as a convex-concave lens having an aspherical first surface when viewed in the light direction.

[0322] The convex lens L6 described in this embodiment has, on its side directed toward the image position IM, f' DOE / f' ges =+35.9 diffractive power f' of DOE This provides in a particularly advantageous manner the minimization of chromatic aberrations over the entire distance adjustment range of the objective lens. For particularly simple manufacture of the diffractive structure, the second surface of lens L6 is configured as a plane in the light direction. The aspherical first surface of lens L5 provides compensation of monochromatic aberrations over the entire distance adjustment range.

[0323] The subgroup G1 of the front group VG is composed of two lenses L1 and L2, and as a whole: f' G1 / f' ges =-9.7 The focal length f' G1 It has.

[0324] In this case, the first lens L1 has a convex-concave shape with negative refractive power, and is configured in a meniscus shape with an aspherically curved convex side and an aspherically curved concave side.

[0325] The small group G2 of the front group VG is f' G2 / f' ges =+5.3 The focal length f' G2 It is advantageous to have

[0326] The focal lengths thus defined for the subgroups G1 and G2 ensure compensation of monochromatic aberrations between the image center and the image field.

[0327] The small group G4 of the rear group HG is composed of a biconvex lens L7 and a biconcave lens L8, which are combined to form a f' G4 / f' ges =+2.5 The focal length f' G4 The doublet is configured as

[0328] In one advantageous embodiment, the subgroup G5 of the rear group HG is f' G5 / f' ges =+0.086 The focal length f' G5 The first concave side of the lens L9 in the light direction is formed as an aspherical surface.

[0329] With the focal lengths defined in this way for the subgroups G4 and G5, coma (aberration), astigmatism and distortion in the image field are further reduced (minimized).

[0330] Advantageously, lens L2 of the front group VG and lens L7 of the rear group HG have the same refractive index. This configuration provides for using the same glass material for both lenses, which in this way facilitates manufacturing and reduces storage costs. To further minimize the Petzval sum, L2 and L7 advantageously have a refractive index of 2.01 (n=2.01) and lens L1 of the front group VG has a refractive index of 1.49 (n=1.49).

[0331] The ratio of the volume V of the focusing group MG to the cube of the image circle diameter Bd at the image plane is 0.05 (V / Bd 3 = 0.05) has proven to be particularly advantageous for high focusing speed in the use of autofocus.

[0332] For the embodiment of FIG. 9, the following table provides the mechanical construction data and optical parameters for each lens element.

[0333] The structural data is the overall focal length f' ges = 1 mm, and for example, for an oval area, the total focal length f' ges = Can be scaled to 28mm.

[0334] In this case, the data relates to surfaces of the lens elements with increasing number in the optical direction. The first surface 1 describes the air-glass transition of lens L1, the last surface 17 describes the glass-air transition of lens L9, and the aperture stop BL is given as a planar (flat) surface 8.

[0335] For each surface, the vertex radius r, i.e., the radius on the optical axis, is given. The third column (from the left) gives the type of surface. For example, K01 indicates that the first surface is an aspherically curved surface, and H12 indicates that the twelfth surface is a diffractive surface. d M indicates the center thickness or the distance to the adjacent surface at the apex of each lens. For the middle group MG, which is configured to be shiftable for focusing, the value d M is given as the distance at the focusing position relative to infinity, and V01 and V02 indicate distances that can be changed by focusing.

[0336] ne indicates the refractive index for the Fraunhofer line e (wavelength 546.0740 nm), and ve indicates the Abbe number for the Fraunhofer line e.

[0337] The correspondence between the consecutively numbered surfaces and the respective lenses L1 to L9, subgroups G1 to G5 and groups VG, MG and HG is given in the last three columns: TIFF0007719181000022.tif104155

[0338] In the following table, the conic constant k and the aspherical coefficients a2 to a6 are given for the aspherical surfaces designated K in the above surface types, and the phase coefficient C1 is given in exponential notation for the diffractive surfaces designated H12: TIFF0007719181000023.tif73138

[0339] 10 shows a schematic diagram of an example of a circular imaging surface IM at the image position. The double arrow indicates the image circle diameter Bd, which overlaps with the diagonal of the image sensor Bs depicted in the rectangle.

[0340] Here, possible embodiments of the present invention are described. [Appendix 1] A fixed focal length objective lens having a front lens group that is fixed in the direction of light, a fixed aperture with an adjustable aperture, a fixed rear lens group, and a focusing group that is shiftable relative to the aperture along the optical axis of the objective lens to image objects at a plurality of different distances onto a fixed image plane. The focusing group is comprised of at least one lens element and a diffractive optical element incorporated into the focusing group. [Note 2] In the above objective lens, The front lens group has positive refractive power; the focusing group is composed of a maximum of two lens elements and has positive refractive power as a whole. [Appendix 3] In the above objective lens, The ratio of the refractive power of the diffractive optical element to the total refractive power of the objective lens is a minimum of 14.9 and a maximum of 45.4. [Appendix 4] In the above objective lens, the ratio of the total refractive power of the focusing group to the total refractive power of the objective lens is a minimum of 0.9 and a maximum of 3.0; The focusing group is composed of only one lens element having an aspherical convex front surface in the optical direction, and a rear surface having a vertex radius configured substantially planar; The ratio of the total refractive power of the focusing group to the vertex radius is a minimum of -0.1255 and a maximum of 0.1388; the substantially planar rear surface carries the diffractive optical element. [Appendix 5] In the above objective lens, The focusing group consists of a single lens element having, in the optical direction, an aspherical convex front surface and a planar rear surface on which the diffractive optical element is arranged. [Appendix 6] In the above objective lens, the ratio of the total refractive power of the focusing group to the total refractive power of the objective lens is at least 0.5 and at most 1.0; The focusing group is composed of a single lens element having an aspherical convex front surface in the optical direction, and a rear surface having a weakly curved apex radius, the apex radius being at least 3.159 mm, but at least 1.013 mm, when the total refractive power is normalized to 1 mm, and the diffractive optical element is arranged on the weakly curved rear surface. [Appendix 7] In the above objective lens, The focusing group is composed of two lens elements arranged sequentially behind the aperture stop in the light direction, the first of which has an aspherical convex front surface, and the second of which has the diffractive optical element arranged on its planar rear surface. [Appendix 8] In the above objective lens, The first lens element has a concave posterior surface; the second lens element has a convex anterior surface. [Appendix 9] In the above objective lens, The focusing group is movable from a position having focusing on an object point at infinity to a position having close distance focusing, in a direction opposite to the light direction, away from the rear lens group and towards the front lens group. [Appendix 10] In the above objective lens, the focusing group is disposed in a near-aperture region in front of or behind the aperture; Between the focusing group and the diaphragm there are either no optical elements or at most one further optical element. [Appendix 11] In the above objective lens, The first lens in the front lens group is configured with an aspherical surface on one or both sides. [Appendix 12] In the above objective lens, The final lens in the rear lens group is constructed with an aspherical surface on one or both sides. [Appendix 13] In the above objective lens, The ratio of the volume V of the focusing group to the cube of the image circle diameter on the image plane is less than 0.1. [Appendix 14] In the above objective lens, The ratio of the optical structure length of the objective lens to the image circle diameter on the image plane is 0.3 or less. [Explanation of symbols]

[0341] BL Aperture Stop L1~L10 Lenses 1~10 G1~G5 1st~5th small group VG front group MG middle group HG rear group Bd Image circle diameter IM Image plane / image position * Aspherically curved lens surface # Diffractive power surface

Claims

1. 1. A fixed focal length objective lens consisting of three optical structural groups, including a fixed front lens group (VG) in the optical direction, a fixed diaphragm (BL) with an adjustable aperture, a fixed rear lens group (HG), and a focusing group (MG) that is shiftable relative to the diaphragm along the optical axis of the objective lens for imaging objects at a plurality of different distances onto a fixed image plane (IM), the focusing group (MG) is composed of at least one lens element and a diffractive optical element (DOE) incorporated in the focusing group (MG); The overall focal length of the objective lens (f' ｇｅｓ ) the total focal length (f') of the focusing group (MG) ＭＧ ) is a minimum of 0.9 and a maximum of 3.0; The focusing group (MG) is composed of only one lens element having an aspherical convex front surface in the optical direction, and the rear surface has a vertex radius (r ＤＯＥ ) The vertex radius (r ＤＯＥ ) the total focal length (f') of the focusing group (MG) ＭＧ ) is at least -0.1255 and at most 0.1388, and the diffractive optical element (DOE) is disposed on the substantially planar rear surface. An objective lens characterized by:

2. 2. The objective lens according to claim 1, The front lens group (VG) has a positive focal length, and the focusing group (MG) has a positive focal length (f' ＭＧ ) An objective lens characterized by:

3. 3. The objective lens according to claim 1, The overall focal length of the objective lens (f' ｇｅｓ ) the focal length (f') of the diffractive optical element (DOE) ＤＯＥ ) ratio is 14.9 at minimum and 45.4 at maximum. An objective lens characterized by:

4. The objective lens according to any one of claims 1 to 3, The focusing group (MG) is composed of a single lens element having an aspherical convex front surface in the optical direction and a planar rear surface on which the diffractive optical element (DOE) is arranged. An objective lens characterized by:

5. 1. A fixed focal length objective lens consisting of three optical structural groups, including a fixed front lens group (VG) in the optical direction, a fixed diaphragm (BL) with an adjustable aperture, a fixed rear lens group (HG), and a focusing group (MG) that is shiftable relative to the diaphragm along the optical axis of the objective lens for imaging objects at a plurality of different distances onto a fixed image plane (IM), the focusing group (MG) is composed of at least one lens element and a diffractive optical element (DOE) incorporated in the focusing group (MG); The overall focal length of the objective lens (f' ｇｅｓ ) the total focal length (f') of the focusing group (MG) ＭＧ ) is a minimum of 0.5 and a maximum of 1.0; The focusing group (MG) consists of only one lens element with an aspherical convex front surface in the optical direction, and its rear surface has a weakly curved apex radius (r ＤＯＥ ) and the vertex radius (r ＤＯＥ ) is the overall focal length (f' ｇｅｓ ) is normalized to 1 mm, the curve is at least 1.013 mm, and the diffractive optical element (DOE) is disposed on the weakly curved rear surface. An objective lens characterized by:

6. 6. The objective lens according to claim 5, The front lens group (VG) has a positive focal length, and the focusing group (MG) has a positive focal length (f' ＭＧ ) An objective lens characterized by:

7. 7. The objective lens according to claim 5, The overall focal length of the objective lens (f' ｇｅｓ ) the focal length (f') of the diffractive optical element (DOE) ＤＯＥ ) ratio is 14.9 at minimum and 45.4 at maximum. An objective lens characterized by:

8. 1. A fixed focal length objective lens consisting of three optical structural groups, including a fixed front lens group (VG) in the optical direction, a fixed diaphragm (BL) with an adjustable aperture, a fixed rear lens group (HG), and a focusing group (MG) that is shiftable relative to the diaphragm along the optical axis of the objective lens for imaging objects at a plurality of different distances onto a fixed image plane (IM), the focusing group (MG) is composed of at least one lens element and a diffractive optical element (DOE) incorporated in the focusing group (MG); The focusing group (MG) is composed of two lens elements (L5, L6) arranged sequentially behind the stop (BL) in the light direction, and of the two lens elements (L5, L6), the first lens element (L5) has an aspherical convex front surface, and the diffractive optical element (DOE) is arranged on the planar rear surface of the second lens element (L6). An objective lens characterized by:

9. 9. The objective lens according to claim 8, The front lens group (VG) has a positive focal length, and the focusing group (MG) has a positive focal length (f' ＭＧ ) An objective lens characterized by:

10. 10. The objective lens according to claim 8, The overall focal length of the objective lens (f' ｇｅｓ ) the focal length (f') of the diffractive optical element (DOE) ＤＯＥ ) ratio is 14.9 at minimum and 45.4 at maximum. An objective lens characterized by:

11. The objective lens according to any one of claims 8 to 10, The first lens element (L5) has a concave rear surface and the second lens element (L6) has a convex front surface. An objective lens characterized by:

12. The objective lens according to any one of claims 1 to 11, the focusing group (MG) is movable from a position with focusing on an object point at infinity to a position with close focusing, in a direction opposite to the direction of light, away from the rear lens group (HG) towards the front lens group (VG); An objective lens characterized by:

13. The objective lens according to claim 12, the focusing group (MG) is disposed in a region near the aperture stop (BL) in front of or behind the aperture stop (BL); Between the focusing group (MG) and the aperture (BL), there is no optical element or at most one further optical element. An objective lens characterized by:

14. The objective lens according to any one of claims 1 to 13, The first lens (L1) of the front lens group (VG) is configured with an aspherical surface on one or both sides. An objective lens characterized by:

15. The objective lens according to any one of claims 1 to 14, The final lens (L7, L8, L9) of the rear lens group (HG) is configured with an aspherical surface on one or both sides. An objective lens characterized by:

16. The objective lens according to any one of claims 1 to 15, The ratio of the volume V of the focusing group (MG) to the cube of the image circle diameter (Bd) on the image plane (IM) is less than 0.1 (V / Bd ３ <0.1) An objective lens characterized by:

17. The objective lens according to any one of claims 1 to 16, The ratio of the optical structure length (SO') of the objective lens to the image circle diameter (Bd) on the image plane (IM) is 3.0 or less (SO' / Bd≦3.0). An objective lens characterized by:

Images