FIXED FOCAL LENGTH LENS WITH CONSTANT LENGTH FOR AUTOFOCUS APPLICATIONS

Description

[0001] The invention relates to an interchangeable lens with a fixed focal length according to the preamble of claim 1. Lenses of this type are known from JP 2012 058682 A, US 2004 / 017605 A1, JP 2007 298832 A, JP 2011 048232 A, US 2016 / 0178875 A1 and US 2011 / 096410 A1.

[0002] Such lenses are familiar from analogue photography for photographic image capture purposes and are also used for digital image capture. Increasingly, digital cameras no longer have a mirror that can be swiveled in and out of the image capture beam path, which redirects the object field to be photographed via a prism into a viewfinder for focusing purposes and to select the image section. Instead, image selection is achieved by continuous image capture with the image sensor and based on an object section obtained from this, displayed on a display on the back of the camera or with the aid of an electronic viewfinder. These lenses focus automatically using electronic autofocus signals and corresponding control of the focusing element in the lens.To achieve good imaging performance, photographic lenses usually consist of two or more lens groups, which in turn have individual lens elements that are mounted stationary or can be moved along the optical axis. It is known to provide a lens group that can be moved along the optical axis to focus the lens on different object distances. This can be, for example, the lens head, i.e. the front lens group facing the object plane, or the entire lens. Such an arrangement is also called overall focusing. With this type of focusing, however, the overall length of the lens changes during focusing, which has disadvantages in terms of tightness. Therefore, lenses are also known in which a lens element that is mounted displaceably within the lens, the so-called focusing element, is moved along the optical axis. Such an arrangement is also called internal focusing.Although lenses of this type can be focused over a wide range from an infinite object distance down to a close range of a few meters or even centimeters, meaning they produce a sharp image of the object on the image recording plane, their optical imaging performance deteriorates particularly at close range. Optical aberrations such as distortion, field curvature, aperture aberration, chromatic aberration, and coma increase. The resulting images often no longer meet the imaging performance requirements of modern image recording systems, even when focused on the desired object distance. However, if high imaging performance is to be achieved, complex and expensive lens designs with a large number of different lenses are necessary.Alternatively, it is known to provide a second movable lens element, a so-called float element, to increase the imaging performance of lenses with total focusing, especially in the close-up range. This element counteracts the imaging errors but otherwise has no influence on the focus position.

[0003] To create lenses with variable focal lengths (zoom lenses), at least two lens elements or lens groups are usually provided, adjustable relative to each other along curves. Focusing is still achieved with a focus element that can be adjusted for focusing. In such known lenses, a group of two lens groups is responsible for changing the focal length, while another lens group is used independently for focusing.

[0004] Such a lens with variable focal length is known, for example, from US 2013 / 0070124 A1. This lens has three movable lens groups for changing the focal length and focus.

[0005] US Pat. No. 8,619,374 B2 discloses an interchangeable lens with variable focal length. A fixed front lens group is followed by an axially adjustable lens group for changing the focal length. Two independently adjustable focusing lens groups are inserted between two further fixed lens groups. The two focusing lens groups are intended to compensate for aberrations that arise depending on the change in focal length.

[0006] The object of the invention was to enable very high, consistent image quality with interchangeable lenses with a fixed focal length when focusing on different object distances from infinity down to the extremely close range of less than 30 cm or with an image scale of up to 1:3. The lenses required for focusing should have a simple, lightweight design in order to achieve a fast and quiet autofocus drive with high acceleration rates. Furthermore, the lenses should be suitable for use on mirrorless recording systems with a short flange focal distance, have a short back focus, and at the same time have a sufficiently large distance between the exit pupil of the lens and the image plane. To be suitable for modern image sensors, the angle of incidence of light in the image plane, viewed from the normal, should not be too large.

[0007] This object is achieved according to the invention by the characterizing features of claim 1. Advantageous further developments emerge from the features of the subclaims.

[0008] Regarding the solution features specified in the claims, it should be noted that modern optical design typically uses automatic correction programs, such as "Code V" from Optical Research Associates. These programs are capable of calculating proposals for functional lens systems with a correction state optimized for a specific task from given lens sequences and refractive power distributions. Targeted modifications of the specified parameters by the optical designer further improve the automatically achieved correction state.

[0009] Using the features of claim 1, the design data for radii, lens thicknesses, lens spacings, refractive indices, and Abbe numbers of the optical glasses to be used can be obtained in this way. By taking into account the features specified in the subclaims, the design parameters can be gradually and specifically improved.

[0010] The drawing shows exemplary embodiments of the lens according to the invention, illustrated to scale. Design data can be found in the tables associated with the respective figures. It is clear to the skilled person, an optical designer, that the design effort for lenses according to the invention is reduced if a lower optical imaging performance is accepted.

[0011] The essential feature of lenses according to the invention consists in providing two focusing lens groups in a lens barrel that are displaceably mounted along an optical axis with respect to an image plane. A front focusing lens group is arranged in front of a fixed center group with lenses and an aperture diaphragm (iris diaphragm), as seen from the object side, and a rear focusing lens group is arranged behind a fixed center group with lenses and an aperture diaphragm (iris diaphragm), as seen from the object side. By controlling the two focusing lens groups together relative to one another and to the other lens groups arranged stationary in the lens barrel, the path of the image aberrations introduced when focusing on different object distances is advantageously mutually compensated. In addition, a lens according to the invention has a front lens group that is stationary when seen from the object side and a rear lens group that is stationary and faces the image plane.In this way, a lens with a fixed focal length is realized, which consists of five lens groups, three of which are fixed and two of which are movable along the optical axis for focusing purposes.

[0012] In contrast to lenses with total focusing with a floating element, with the focusing according to the invention (hereinafter also referred to as double focusing), the two focusing lens groups jointly shift the focus position to focus the object plane onto the image plane. The travel of the focusing groups for focusing from infinity to the close-up setting (maximum travel corresponds to the total travel) is limited by the mechanical length of the lens and the motor / drive concept of the autofocus. The ratio of the two respective total travels to one another can be 1 or not. It results from design-related spatial restrictions and can be varied to optimize aberrations. According to the invention, the front lens group and the rear lens group have negative refractive power, or the front lens group and the rear lens group have positive refractive power.In an alternative embodiment, the front lens group has positive refractive power and the rear lens group has negative refractive power, or the front lens group has negative refractive power and the rear lens group has positive refractive power.

[0013] In a special embodiment of the lenses, both the front focusing group G2 and the rear focusing group G4 have positive refractive power and move away from the image plane IM when focusing from infinity to the close-up setting.

[0014] For 35mm format lenses with focal lengths between 55mm and 185mm, for example, it is advantageous to use more lenses with positive refractive power than with negative refractive power in the front lens group, whereby the front lens group has a positive overall refractive power.

[0015] In the case of lenses according to the invention with central groups of positive total refractive power, a favorable distribution of the refractive powers in the rear assembly and compliance with design specifications are ensured, which result, for example, from the specified maximum external dimensions of the lens, the specified maximum aperture and lens diameters and from the restrictive dimensions of a camera bayonet, in particular its free internal diameter.

[0016] An embodiment of a lens according to the invention is shown in Fig. 9 shown in the drawing and is based on the Fig. 9 described in more detail in the table with focal length information [f'] for the five lens groups and refractive power values ​​[Dpt.].

[0017] The Figures 1 to 8 with associated tables and associated description serve to explain the basic structure of five lens groups with two focus groups and are not part of the present invention.

[0018] In this way, it is possible to produce, for example, a 24mm, 50mm or 90mm lens with an aperture of 2.0, or even a 50mm lens with an aperture of 1.4, whereby the focal length specification in this case refers to the 35mm format (image circle diameter 43.3 mm). It is possible for a person skilled in the art to produce lenses with smaller (down to 0.9, for example) or larger (4.0, for example) apertures, provided the parameters specified in the patent claims are observed. With a smaller aperture, the design effort increases, which has adverse effects on the lens volume, the number of lenses required and the lens diameters if the optical imaging performance (aberrations) is not to be reduced too much. With a larger aperture, on the other hand, the design effort usually decreases while the imaging performance remains the same or is poorer.

[0019] Scaling the geometric data of the lens to other image formats is possible while maintaining the respective aperture, resulting in a corresponding scaling of the focal length. Lenses realized in this way, with otherwise identical design features, are also subject to the invention.

[0020] In a particular embodiment of the lens according to the invention, the ratio f1 / f of the focal lengths f1 of the front lens group and f of the entire lens is between -40 and 30, the ratio f2 / f of the focal lengths f2 of the front focusing group and f of the entire lens is between -10 and 20, the ratio f3 / f of the focal lengths f3 of the middle group and f of the entire lens is between -30 and 40, the ratio f4 / f of the focal lengths f4 of the rear focusing group and f of the entire lens is between -10 and 20 and the ratio f5 / f of the focal lengths f5 of the rear lens group and f of the entire lens is between -40 and 30.

[0021] In a first optimization step of the ratio f1 / f, limiting it to a range between -2.0 and -0.8 or between 0.4 and 5.0 has proven advantageous. To avoid excessive sensitivity with regard to assembly tolerances to be maintained, it is particularly advantageous to limit the ratio downwards (small values ​​in terms of magnitude), and to achieve the most compact size possible, the ratio f1 / f must be limited upwards (large values ​​in terms of magnitude). An embodiment of the invention optimized with regard to assembly tolerances and size therefore has a ratio f1 / f of -1.7 and -1.0 or values ​​in between, or of 0.5 and 2.1 or values ​​in between.

[0022] In a particular embodiment of the lens according to the invention, a reduction in the focusing travel of the front focusing group and the overall length of the lens can be achieved by limiting the f2 / f ratio to a range between -1.0 and -0.3 or between 1.0 and 10.0. In general, small focusing travels are advantageous for fast focusing, but they also increase tolerance sensitivity. A focusing travel that is too large, on the one hand, increases the overall length and, on the other hand, requires powerful and fast motor drives with high energy consumption for focusing. For double focusing according to the invention, limiting the f2 / f ratio to -0.7 and -0.4 or 1.3 and 5.6, or a range between one of the two aforementioned ranges, is therefore particularly advantageous.

[0023] An advantageous optimization carried out in the same way for the focusing rear group is shown by restricting the ratio f4 / f to a range between -5.0 and 5.0, whereby a further optimization can be achieved by restricting it to -1.9 and -0.8 or to 0.6 and 0.9, or a range between -1.9 and -0.8 or between 0.6 and 0.9.

[0024] An advantageous design of the lenses of the middle group with regard to manufacturing tolerances and size is achieved by limiting the ratio f3 / f to a range between -2.0 and -0.5 or 0.2 and 5.0, with an optimization according to the invention being at a ratio f3 / f of -1.2 and -1.0 or 0.4 and 3.4, or in a range between -1.2 and -1.0 or between 0.4 and 3.4.

[0025] Large values ​​of the f5 / f ratio of the rear lens group result in an unfavorably large overall length, while small values ​​make the lens group sensitive to assembly tolerances. Therefore, an advantageous optimization consists in limiting the f5 / f ratio to a range between -28.0 and -0.6 or between 0.5 and 10.0. Particularly with lenses for mirrorless cameras, where experience shows that the distances between the last lens in the direction of light (located near the image plane) and the image plane are very short, it is advantageous not to make the angle of incidence too large, viewed from the perpendicular to the image plane. An angle of incidence of less than 35° has proven advantageous. The lenses are therefore particularly suitable for camera systems with a short flange focal length and short back focus, e.g., less than 25mm, relative to the 35mm format described above.Therefore, values ​​of the f5 / f ratio that are too small have a disadvantageous effect, as they increase the angle of incidence and thus increase vignetting. A lens version optimized for this problem therefore has f5 / f ratios of -21.0 and -0.8, or 0.8 and 5.2, or a value somewhere in between.

[0026] In a further development according to the invention, the lens has a ratio of the total focal length f to the image circle diameter in the image plane (IM) between 0.3 and 5. In this way, lenses with a sufficiently large distance between the exit pupil and the image plane, e.g. greater than 40 mm, and with a focal length between 13 mm and 216.5 mm, based on the previously described 35 mm format, can be realized.

[0027] Lightweight focusing groups are advantageous for high focusing speed. The ratio of the volume V of the front and rear focusing groups to the image circle diameter in the image plane is less than 0.1 to the third power (V / Bd3 < 0.1) and, in particular, less than 0.08 (V / Bd3 < 0.08). It is particularly advantageous for the respective focusing group to have a weight of less than 10 g (grams).

[0028] The relative volume value of 0.08 then corresponds, based on the 35mm format, to a weight of 23.2 g for a light lens, such as the Schott N-PSK53A, and 35.8 g for a heavy lens, such as the Schott N-LASF31A. For medium format systems with a 1.5x larger image circle diameter, this results in lens weights of 78.3 g for a light lens and 120.8 g for a heavy lens. For APS systems with a 1.5x smaller image circle diameter, this results in lens weights of 6.9 g for a light lens and 10.6 g for a heavy lens.

[0029] A low weight is beneficial for the focusing speed and has a positive effect on motor and noise concepts.

[0030] In a particular embodiment of a lens, the front lens group consists of four lens elements, the first lens element, the second lens element, and the third lens element having positive refractive power, and the fourth lens element having negative refractive power, the third lens element and the fourth lens element being combined to form a lens doublet with negative total refractive power. An embodiment with a front lens group according to the invention is available as a lens 1:2 90mm and 1:2 75 in Fig. 1 and 2 shown in the drawing and is described in more detail using the associated tables with focal length information [f'] and refractive power values ​​[Dpt.].

[0031] The front lens group of an alternative lens consists of four lens elements, with the first lens element and the second lens element having positive refractive power, the third lens element having negative refractive power, and the fourth lens element having positive refractive power. Either the third lens element and the fourth lens element are combined to form a lens doublet with a negative total refractive power, or the second lens element, third lens element, and the fourth lens element are combined to form a cemented element with a positive total refractive power. In the drawing, Fig. 6 and Fig. 7 More detailed examples of implementation, which are described in more detail as 1:2 90mm lenses using the associated tables with focal length information [f'] and refractive power values ​​[Dpt.].

[0032] In another embodiment, the front lens group also consists of four lens elements, with the first lens element and the second lens element having negative refractive power, the third lens element having positive refractive power, and the fourth lens element having negative refractive power. In this example, the third and fourth lens elements are combined to form a lens doublet with a negative total refractive power. In the drawing, Fig. 5 with the associated table a 1:2.0 24mm lens with exact group focal lengths and refractive power values ​​is specified.

[0033] The front lens group consists of a single lens element with either negative or positive refractive power. For this example, Fig. 4 a 1:2.0 50mm and Fig. 8 a 1:1.4 50mm lens and more precise values ​​are given in the respective tables.

[0034] In a further embodiment of the lens according to the invention, the front lens group consists of two lens elements, the first lens element having positive refractive power and the second lens element having negative refractive power, and both are combined to form a lens doublet with positive total refractive power. Fig. 9 The drawing shows a corresponding embodiment, which is described in more detail as a 1:1.4 50mm lens using the associated table.

[0035] In a further embodiment of a lens, the front lens group consists of three lens elements, with the first and second lens elements having negative refractive power, and the third lens element having positive refractive power. The second and third lens elements are combined to form a lens doublet with a negative total refractive power. In the drawing, Fig. 3 an example of a 1:2.0 50mm with the corresponding table is described in more detail.

[0036] In an advantageous embodiment of a lens, the center group consists of a lens element of positive refractive power, with the iris diaphragm AP being fixedly arranged in front of it. In the drawing, Fig. 7 an example of a 1:2.0 50mm with associated table more precisely

[0037] In a further development of the middle group, this consists of two lens elements, whereby the first lens element has negative and the second lens element has positive refractive power and the iris diaphragm AP is fixedly arranged between the first and second lens elements. Figures 1 and 2 show such a middle group.

[0038] In an alternatively optimized version of the center group, it consists of three lens elements, with the first lens element having negative, the second lens element positive, and the third lens element positive refractive power. The first and second lens elements are combined to form a lens doublet with a positive total refractive power, and the iris diaphragm AP is in a Fig. 5 In the example shown, it is arranged stationary between the lens doublet and the third lens element.

[0039] In a further middle group consisting of three lens elements, the first lens element has negative refractive power, the second lens element has positive refractive power, and the third lens element has negative refractive power. The second and third lens elements are combined to form a lens doublet with a positive total refractive power. Fig. 6 shown example and the iris diaphragm AP is arranged stationary in front of the first lens element.

[0040] In an alternative embodiment, the center group consists of four lens elements, with the first lens element having positive refractive power, the second negative refractive power, and the third and fourth lens elements having positive refractive power. The second and third lens elements are combined to form a lens doublet with a positive total refractive power, with the iris diaphragm AP being fixedly positioned in front of the first lens element. Figure 3 shows such an embodiment.

[0041] In Figure 4An embodiment with a central group consisting of five lens elements is shown. The first lens element has positive refractive power, and the second lens element has negative refractive power; both are combined to form a lens doublet with a negative total refractive power. In this embodiment, the third lens element has negative refractive power, and the fourth lens element has positive refractive power, both being combined to form a lens doublet with a positive total refractive power. The fifth lens element has positive refractive power, and the iris diaphragm AP is fixedly arranged between the two lens doublets.

[0042] In an alternative embodiment, the center group consists of six lens elements, the first lens element having positive refractive power and the second lens element having negative refractive power, and both are combined to form a first lens doublet with a negative total refractive power. The third lens element has positive refractive power, the fourth lens element has negative refractive power, and the fifth lens element has positive refractive power, with the fourth and fifth lens elements being combined to form a second lens doublet with a negative total refractive power. The sixth lens element has positive refractive power. Figures 8 and 9 In the example shown, the iris diaphragm AP is arranged stationary between the first lens doublet and the third lens element.

[0043] In a particular embodiment of the objective according to the invention, the rear lens group consists of three lens elements, the first lens element having positive and the second lens element having negative refractive power, and both are combined to form a lens doublet with negative total refractive power. The third lens element has Fig. 9 The illustrated embodiment has negative refractive power.

[0044] In a further embodiment of the lens, the rear lens group also consists of three lens elements, the first lens element having positive and the second lens element having negative refractive power, and both are combined to form a lens doublet with positive total refractive power. Fig. 3 In the embodiment shown, the third lens element has positive refractive power.

[0045] An alternative embodiment has a rear lens group with two lens elements. Figures 1 , 2and 7 The embodiments shown have positive refractive power in the first lens element and negative refractive power in the second lens element.

[0046] A rear lens group consisting of only one lens element with negative refractive power is in each case Figures 4 , 5 and 6 shown as an example.

[0047] Particularly advantageously, one or more lens elements with one or two aspherical surfaces can be provided for the correction of monochromatic aberrations such as spherical aberrations, coma, astigmatism, curvature and distortion.

[0048] In the embodiments shown in the drawing, these are in the Figures 3 , 4 , 5 , 6 , 7 , 8 and 9 marked with an *.

[0049] To ensure a short back focus suitable for mirrorless systems (e.g., less than 25mm, based on the 35mm format) and an exit pupil position suitable for image sensors, the rear lens groups can contain at least one lens made of an optical material with a refractive index ne greater than 1.8. This also allows for compliance with restrictions on the maximum diameter of the lenses due to diameter limitations specified by the camera or image capture system, e.g., a bayonet mount.

[0050] The five lens groups shown and described individually represent a necessary, self-contained component in all lens variants. Each of the lens groups can be optically adjusted individually, which is particularly reflected in the focal length ratio to the total focal length specified for each lens group.

[0051] In the drawing, embodiments of the lenses according to the invention for the 35mm format are shown schematically and are described in more detail below with reference to the figures.

[0052] Show Fig. 1 a lens section through a lens with a focal length of 90mm and an open aperture of 2, Fig. 2 a lens section through a lens with a focal length of 75mm and an open aperture of 2, Fig. 3 and 5 a lens section through a lens with a focal length of 24mm and an open aperture of 2, Fig. 4 a lens section through a lens with a focal length of 50mm and an open aperture of 2 Fig. 6 and 7 a lens section through a lens with a focal length of 90mm and an open aperture of 2, Fig. 8 and 9 a lens section through a lens with a focal length of 50mm and an open aperture of 1.4, Fig. 10 an image sensor in an image plane IM.

[0053] The lens sections in the figures show the movement paths of the respective lens groups during the focusing process. Horizontal lines represent the positions of lens groups G1, G2, G3, G4, and G5. The upper lines indicate the positions at the infinity focus setting, the lower lines at the closest object distance, and the middle lines at a medium focus setting. The vertical lines correspond to the fixed lens groups G1, G3, and G5, and the oblique lines to the movable focusing groups G2 and G4.

[0054] The lens sections in the drawing are shown to scale, so that relative information, such as the Fig. 1 In the lens element G5L2, the material thickness in the center of the lens is considerably thinner than the material thickness at the edge of the lens, which can be graphically determined and verified using conventional geometric means. It is also revealed in this way that in Fig. 1the lens element G1L2 has a material thickness in the center of the lens that is almost exactly 2 times (2.11 times) thicker than the lens element G1L1. These relationships are readily apparent to the person skilled in the art, so that lens geometries can also be derived. For example, in Fig. 1 shown that the first lens group G1, seen from the object side, is constructed from a sequence, seen in the direction of light to the image plane IM, of two convex-concave lenses of positive refractive power, spaced approximately by the thickness of the first lens G1L1, to which a cemented element with a smaller spacing is assigned below, which consists of a biconvex lens of positive and a biconcave lens of negative refractive power.

[0055] Concrete examples of implementation can be found in the following tables for lenses with 90mm, 75mm, 50mm and 24mm focal lengths with an aperture of 2 and two lenses with 50mm focal length and an aperture of 1.4, whereby the focal lengths are each related to the well-known small film format (43.3mm image circle diameter). Fig. 1 2 / 90 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 176,5 5,7 2,0 + G2 55,0 18, 2 0,6 + G3 -91,0 -11,0 -1,0 - G4 -90,4 -11,1 -1,0 - G5 72,1 13,9 0,8 + Fig. 2 2 / 75 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 159,1 6,3 2,1 + G2 55,0 18, 2 0,7 + G3 -91,0 -11,0 -1,2 - G4 -96,1 -10,4 -1,3 - G5 72,1 13,9 1,0 + Fig. 3 2 / 24 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 -36,5 -27,4 -1,5 - G2 133,2 7,5 5,6 + G3 18,0 55,6 0,8 + G4 -24,9 -40,2 -1,0 - G5 125,6 8,0 5,2 + Fig. 4 2 / 50 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 -83,9 -11,9 -1,7 - G2 63,0 15,9 1,3 + G3 29,9 33,5 0,6 + G4 -66,1 -15,1 -1,3 - G5 -84,8 -11,8 -1,7 - Fig. 5 2 / 24 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 -37,6 -25,6 -1,6 - G2 105,1 9,5 4,4 + G3 18,4 54,3 0,8 + G4 -42,4 -23,6 -1,8 - G5 -499,2 -2,0 -20,8 - Fig. 6 2 / 90 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 64,9 15,4 0,7 + G2 -61,3 -16,3 -0,7 - G3 32,4 30,9 0,4 + G4 -76,5 -13,1 -0,8 - G5 -111,2 -9,0 -1,2 - Fig. 7 2 / 90 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 53,1 18,8 0,6 + G2 -36,4 -27,5 -0,4 - G3 78,8 12,7 0,9 + G4 79,8 12,5 0,9 + G5 -68,0 -14,7 -0,8 - Fig. 8 1.4 / 50 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 80,9 12,4 1,6 + G2 -78,5 -12,7 -1,6 - G3 56,7 17,6 1,1 + G4 108,4 9,2 2,2 + G5 -87,9 -11,4 -1,8 - Fig. 9 1.4 / 50 Focal length f' [mm] Refractive power [Dpt.] f'Gr / f' Construction G1 581,0 1,7 11,6 + G2 95,1 10,5 1,9 + G3 62,5 16,0 1,3 + G4 106,3 9,4 2,1 + G5 -104,3 -9,6 -2,1 -

Claims

1. Objective of fixed focal length, consisting of five lens groups, wherein three (G1, G3, G5) are spatially fixed and two (G2, G4) are moveable along an optical axis, characterized in that a) a first, as viewed from one object side, front lens group (G1) having a positive refractive power is arranged spatially fixed, b) a second lens group as a focusing front group (G2) having a positive refractive power is arranged movably, c) a third lens group having a positive refractive power, which comprises a spatially fixed iris diaphragm (AP) that is adjustable in terms of its opening, as a central group (G3) is arranged spatially fixed, d) a fourth lens group as a focusing rear group (G4) having a positive refractive power is arranged movably, and e) a fifth rear lens group (G5) having a negative refractive power is arranged spatially fixed with respect to an imaging plane (IM) in an objective tube, and both the focusing front group (G2) as a single lens and the focusing rear group (G4) as a single lens for focusing the objective on objects at different object distances are movable together relative to each other and to the spatially fixed lens groups (G1, G3, G5), and the spatially fixed iris diaphragm (AP) is arranged between a first lens doublet (G3L1, G3L2) and the third lens element (G3L3) of the central group.

2. Objective according to Claim 1, characterized in that both the focusing front group (G2) and the focusing rear group (G4) move away from the imaging plane (IM) when focusing from infinity into the near setting.

3. Objective according to either of the preceding claims, characterized in that a) the ratio f1 / f of the focal lengths f1 of the front lens group (G1) to f of the entire objective is in the range between 0.5<=f1 / f<=2.1, b) the ratio f2 / f of the focal lengths f2 of the focusing front group (G2) to f of the entire objective is in the range between 1<=f2 / f<=10, c) the ratio f3 / f of the focal lengths f3 of the central group (G3) to f of the entire objective is in the range between 0.2<=f3 / f<=5.0, d) the ratio f4 / f of the focal lengths f4 of the focusing rear group (G4) to f of the entire objective is in the range between 0.6<=f4 / f<=0.9, e) the ratio f5 / f of the focal lengths f5 of the rear lens group (G5) to f of the entire objective is in the range between -28<=f5 / f<=-0.6.

4. Objective according to any of the preceding claims, characterized in that the objective has a ratio of the total focal length f to the image circle diameter in the imaging plane (IM) between 0.3 and 5.

5. Objective according to any of the preceding claims, characterized in that the ratio V of the volume of the respective focusing elements (G2, G4) to the image circle diameter (Bd) in the imaging plane (IM) in the third power is less than 0.1 (V / Bd3<0,1), in particular less than 0.08, or the weight of the respective focusing group (G2, G4) is less than 15 g (grams) .

6. Objective according to one of the preceding claims, characterized in that either a) the front lens group (G1) consists of a lens element which has a positive refractive power, or b) the front lens group (G1) consists of two lens elements (G1L1, G1L2), wherein the first lens element (G1L1) has a positive and the second lens element (G1L2) has a negative refractive power, which are combined to form a lens doublet (G1L1, G1L2) with a positive total refractive power.

7. Objective according to any of the preceding claims, characterized in that the central group (G3) consists of six lens elements (G3L1, G3L2, G3L3, G3L4, G3L5, G3L6), wherein the first lens element (G3L1) has a positive and the second lens element (G3L2) has a negative refractive power and both are combined to form a lens doublet (G3L1, G3L2) with a negative total refractive power, the third lens element (G3L3)has a positive, the fourth lens element (G3L4) has a negative and the fifth lens element (G3L5) has a positive refractive power, and the fourth and fifth lens element are combined to form a lens doublet (G3L4, G3L5) with a negative total refractive power, and the sixth lens element (G3L6) has a positive refractive power.

8. Objective according to any of the preceding claims, characterized in that the rear lens group (G5) consists of three lens elements (G5L1, G5L2, G5L3), wherein the first lens element (G5L1) has a positive, the second lens element (G5L2) has a negative refractive power and both are combined to form a lens doublet (G5L1, G5L2) with a negative total refractive power, and the third lens element (G5L3) has a negative refractive power.