Optical assembly, objective, image acquisition device and apparatus comprising the same

Abstract

An optical assembly (1), an objective, an image capturing device and an apparatus comprising the same are described, the optical assembly comprising a central axis (2), an object side (3), an image side (4) and a catadioptric assembly (10), wherein the optical assembly (1) has a maximum of 25 millimeters of a construction space and a maximum of 60% of a linear vignetting along the central axis (2) from the object side (3) to the image side (4).

Description

TECHNICAL FIELD

[0001] The present application relates to an optical assembly, to an objective (in particular for a microscope, a camera and / or a projector), to an image acquisition device, to an image reproduction device, and to a device (in particular a mobile device). BACKGROUND

[0002] In document DE 2 157 058 A a catadioptric lens-objective for common object- and image-side imaging is disclosed. This assembly is referred to in the document as "catadioptric". In contrast thereto, for the purposes of the present application a catadioptric assembly is understood to be an assembly comprising a first mirror having converging refractive power and a subsequent mirror having diverging refractive power.

[0003] Modern mobile phones usually have one or more integrated cameras with which high-quality images or videos can be taken. These cameras are almost exclusively mounted on the front and back of the mobile device, with the optical axis of the associated optics being oriented perpendicular to the front and back. It follows that the structural length of the optical system is given by the thickness of the mobile device (for example a mobile phone). Typical values here are 6 mm to 8.5 mm.

[0004] In the above-mentioned structural space, optical systems can be realized whose focal length is comparable to the length L of the structural space (i.e. the thickness of the mobile device). The focal ratio F = L / f', i.e. the ratio of the structural length L to the focal length f', is approximately 1. Telephoto structures (i.e. systems whose focal length is greater than the structural space or F < 1) or inverse-telephoto structures (i.e. systems whose focal length is smaller than the structural length or F > 1) can only be realized with great difficulty. Therefore, a solution for increasing the focal length of the optics is sought in order to meet the users' requirements for better objectives.

[0005] Furthermore, it is sought to image near objects in a microscopically enlarged manner using the mentioned cameras. In order to ensure good illumination, a large working distance must be realized. Furthermore, the objects should be imaged with an imaging ratio close to 1:1. Due to these two requirements, the structural length of the objective must be comparable to the front working distance, which leads to the fact that the conventional structural space is not sufficient for this. Therefore, a solution is sought for realizing a longer focal length or a longer structural length on a shorter structural space.

[0006] The microscope objective can in particular be configured as a catadioptric objective (reflex objective). Prior art in this regard is disclosed, for example, in “Lexikon der Optik- Mikroskopobjektive” [Lexicon of optics - microscope objectives] https: / / www.spektrum.de / lexikon / optik / mikroskopobjektiv / 2067, US 10877244 B1, US 2019 / 0187446 A1, US 6169637 B1 and US 5930055 A. The folding of the beam path along the optical axis can be carried out, for example, by means of a Cassegrain, Gregory, Schwarzschild or Maksutov type of catadioptric objective. While the Schwarzschild system leads to a rather large vignetting, the Petzval sum is no longer corrected in the Cassegrain and Gregory type of astronomical telescope. The design structures mentioned have been applied in classic photography, in particular in long focal length objectives. These design types have also been applied in mobile phone applications. Examples in this regard are disclosed in US 10 877 244 B1 and US 2019 / 187446 A1.

[0007] The catadioptric assembly in principle constitutes a strong telephoto structure, which telephoto structure is composed of a first mirror with converging refractive power and a subsequent mirror with diverging refractive power. This sequence of refractive powers forms a catadioptric telephoto structure and thereby shortens the construction length of the objective with respect to the nominal focal length. In addition, the optical path is folded in the direction of the optical axis by using reflective components, which also shortens the construction length. Overall, the catadioptric assembly can achieve a very small telephoto factor F. In order to reduce the vignetting of the catadioptric system, the individual refractive powers of the mirrors have to be adjusted. This, however, leads to the fact that the catadioptric basic system is no longer corrected for all aberrations, so that additional optical correction elements have to be used. In the documents mentioned, these are aspherical lenses, which are arranged behind the catadioptric assembly, i.e. between the catadioptric assembly and the image plane, as seen in the direction of light propagation.

[0008] In order to be able to design the optical system compact, the correction lens elements even partially protrude into the mirror intermediate space, which leads to challenges in terms of mounting technology. In addition, the front and back faces of the catadioptric lens groups in the documents mentioned have undesired jump edges.

[0009] With further development of smart phones, so-called "CMOS imaging sensors" (CIS) with ever smaller pixel sizes and efficient integrated image processing are available. Microscopes can also benefit therefrom in terms of realizing compact and cost-effective systems. Thereby, in particular, imaging with a scale of approximately 1 : 1 can be realized in the range of an average resolution of a few micrometers. If the pixel size is, for example, 1 pm (edge length), a resolution of up to approximately 2 pm can be achieved at an imaging scale of 1 : 1 according to the Nyquist theorem. Naturally, a reduced optics can still achieve a higher resolution.

[0010] If imaging takes place from an object space in air into an image space in air, imaging 1 : 1 has the peculiarity that not only surface elements, but also entire volume elements can be mapped onto one another with high imaging quality. Here, the object space is understood to be the spatial region of at least one object plane or a plurality of object planes in which the imaging optics is present, and the image space is understood to be the spatial region of at least one image plane or a plurality of image planes in which the imaging optics is present. Thus, the goal is to realize volume imaging using a simpler method.

[0011] For the purpose of explaining the technical background, a rotationally symmetrical system will be considered in the following. It is also assumed that the aperture error of the optical system has been corrected. Then the pixel in the center of the image field can be imaged without aberrations. If a small area around the image center is to be transmitted without aberrations, further conditions must also be placed on the optical system. As a rule, the lateral extension of the object is considered, i.e. it is desired to image a planar object perpendicular to the optical axis. This is the case, for example, in photography. There the sine condition must be corrected. The sine condition states that the sine of the angle of the aperture beam to the optical axis is in a fixed ratio to the angle of the aperture beam to the optical axis in the object-image plane:

[0012]

[0013] Here, n is the refractive index of the respective medium, u is the angle of the beam to the optical axis, and β is the imaging scale of the system. The quantities with an apostrophe refer to the image space, the quantities without an apostrophe refer to the object space. The ratio β must apply to all apertures of the system, i.e. to all possible openings up to a maximum number.

[0014] A less considered case is the imaging of the axial extension of the object along the optical axis. Then the so-called Herschel condition must be met, which can be formulated as follows:

[0015]

[0016] The sine condition and the Herschel condition can only be met simultaneously if the edge beam angles of the object space and the image space apply to the following condition:

[0017] |u| = |u'|

[0018] The lateral scale β and the depth scale α in the nominal image plane are thus derived:

[0019] and

[0020] If object and image are in air, then the following applies:

[0021] | α | = | β | = 1

[0022] If the object is in a water solution (n ~ 1.334, n' = 1), then on the other hand | α | = | β | ~ 1.334 applies.

[0023] The sine condition and the Herschel condition are thus the necessary prerequisite conditions for the object to be imaged without aberrations in the vicinity of or close behind or in front of the middle image point in the nominal object plane. They are thus the prerequisite conditions for volume imaging.

[0024] However, the simultaneous satisfaction of the sine condition and the Herschel condition does not yet say anything about the similarity of object and image, i.e. whether a cuboid-shaped object is also imaged as a cuboid.

[0025] The following considerations form the basis for the sub-areas of the present application and are at the same time an integral part of the present application. In order to ensure the above additional conditions, the principal beam angles in the object space and the image space must also still be adapted to one another. If object and image are in air, then γ should be the (geometric) principal beam angle at the object. There is then a depth scale | α | = 1. If the intercept at the object is thus changed by a value Δs0= d0, then the image plane must be focused back by a value Δs1= -d0.

[0026] The principal beam of the original imaging thus generally intersects the object plane at different heights. In order to ensure a true volume imaging, the principal beam in the image space must intersect the object plane at the same modified height. This is only possible if the sum of the principal beam angles before and after the optics vanishes (γ + γ' = 0). This relationship is shown in Figure 1 In a simple symmetrical 1 : 1 system, the nominal imaging is given by A0 -> A0'. If the object intercept is changed and the sine condition and the Herschel condition are satisfied, then A1 -> A1' is imaged with the same principal beam. It is however apparent that the imaging no longer describes a 1 : 1 imaging. The cuboid is imaged as a truncated pyramid.

[0027] However, if the principal beam angles in the object space and the image space are appropriately adapted to one another, then the modified imaging is again a 1 : 1 imaging. In the present exemplary case, this can be achieved for example by the targeted use of field lenses. Here, the volume imaging again achieves a 1 : 1 imaging, so that the cuboid is imaged as a cuboid.

[0028] This relationship also applies to a generalization of any media n, n' in the object-image space, the sum of the geometric angles of the chief ray in the object and in the image must be zero. Here, the signed imaging ratio can be incorporated into the equation and thereby the sign is ensured to be correct.

[0029] n • γ = β • n' • γ'

[0030] In other words, the converging chief ray at the object must become the converging chief ray at the image and vice versa. A special case is that the chief ray angles on the object side and on the image side vanish (γ = γ' = 0). Then a double telecentric optical device is involved. However, a double telecentric optical device is disadvantageous in the field of application of mobile phone optics, since it increases the diameter of the optical device part as well as the construction length.

[0031] A microscopy imaging by inverting a mobile phone objective in front of a smartphone camera is described in Switz et al. Low-Cost Mobile Phone Microscopy with a Reversed Mobile Phone Camera Lens. Plos One, Volume 9, Issue 5, e95330 (May 2014) and Diederich et al. Using machine-learning to optimize phase contrast in a low-cost cell-phone microscope, Plos One, March 1 (2018) (https: / / joumals.plos.org / plosone / article?id=10.1371 / journal.pone.0192937). However, it does not concern a telecentric system. The main beam is converging on the object side by symmetry, while it is diverging on the image side, thus violating the main beam angle condition, so that a cubical volume is imaged as a truncated pyramid volume. A structure composed of micro- objectives is used in Botcherby et al. Aberration-free optical refocusing high numerical aperture microscopy, Optics letters, Vol 32, No 14, pg. 2007-2009 (2007) to produce an intermediate image with 1 : 1 magnification.

[0032] Optics for mobile phone cameras almost exclusively comprise pure lens systems integrated in the smallest space of a mobile phone. Here, the entire system has to be integrated into the thickness of a mobile phone, which is typically 5 mm or 6 mm. The achievable focal length corresponding to the short optical system can then be comparable to the construction length of the optical system or even shorter, for example between 3 mm and 4 mm (cf. US 7 643 225 B1 and McGuire Jr., James P., Manufacturable mobile phone optics: higher order aspheres are not always better, Proc. SPIE 7652, International Optical Design Conference 2010, 765210 (9 September 2010), doi: 10.1117 / 12.871016). The use with typical receiver dimensions, for example a diagonal of approximately 4 mm, therefore results in a "effective focal length" of a wide-angle objective which is far less than 50 mm in terms of its properties. This is accepted by the user for landscape photography. The effect of a long focal length is achieved by digital zoom. Nonetheless, it is desirable to install a real long-focus objective on a mobile phone or smartphone, for example for portrait or long-focus photography. This requires a longer focal length, which is not compatible with the compact construction space.

[0033] As mentioned above, there is the possibility of also effectively using the construction space with a centered optical system by folding the beam path along the optical axis. However, the result is the production of a pupil obscuration, i.e. a central portion of the optical system pupil receives no light.

[0034] The obscuration is typically given by the ratio of the shadow diameter to the diameter of the object pupil. In Figure 2 is shown how the obscuration is calculated. First, consider the imaging of the field center by the open beam 17. In the course through the optical system, the beam R1 sweeps over the subsequent surfaces, in Figure 2In the case of a collimated light input (telescopic imaging), this is the ratio of the height of R1 and R0 in the entrance pupil, i.e. the ratio of the numerical aperture of the telescope. In the case of a finite light input (projection objective), this is the ratio of the directional cosines rvl0 of the beam R1 and rvl1 of the beam R0. The directional cosine rvl0 of the beam R0 here gives exactly the numerical aperture of the object space. It is desirable that the vignetting can be kept as small as possible. For this, the following reasons are decisive. The greater the vignetting, the more light is blocked, which leads to the need for longer exposure times. This effect is quadratic in the vignetting. The greater the vignetting, the lower the contrast of the imaging of monotone structures, and thus the relevant image contrast, which is characterized by the modulation transfer function MTF. This effect is linear in the vignetting. Furthermore, the vignetting at the point of the out-of-focus image, i.e. the high light, can unpleasingly notice the "doughnut" effect. Figure 2 In the case of a collimated light input (telescopic imaging), this is the ratio of the height of R1 and R0 in the entrance pupil, i.e. the ratio of the numerical aperture of the telescope. In the case of a finite light input (projection objective), this is the ratio of the directional cosines rvl0 of the beam R1 and rvl1 of the beam R0. The directional cosine rvl0 of the beam R0 here gives exactly the numerical aperture of the object space. It is desirable that the vignetting can be kept as small as possible. For this, the following reasons are decisive. The greater the vignetting, the more light is blocked, which leads to the need for longer exposure times. This effect is quadratic in the vignetting. The greater the vignetting, the lower the contrast of the imaging of monotone structures, and thus the relevant image contrast, which is characterized by the modulation transfer function MTF. This effect is linear in the vignetting. Furthermore, the vignetting at the point of the out-of-focus image, i.e. the high light, can unpleasingly notice the "doughnut" effect.

[0035] In the case of a finite light input (projection objective), this is the ratio of the directional cosines rvl0 of the beam R1 and rvl1 of the beam R0. The directional cosine rvl0 of the beam R0 here gives exactly the numerical aperture of the object space. It is desirable that the vignetting can be kept as small as possible. For this, the following reasons are decisive. The greater the vignetting, the more light is blocked, which leads to the need for longer exposure times. This effect is quadratic in the vignetting. The greater the vignetting, the lower the contrast of the imaging of monotone structures, and thus the relevant image contrast, which is characterized by the modulation transfer function MTF. This effect is linear in the vignetting. Furthermore, the vignetting at the point of the out-of-focus image, i.e. the high light, can unpleasingly notice the "doughnut" effect.

[0036] Catadioptric photographic objectives are disclosed, for example, in documents US 4 714 307 B1 and US 6 169 637 B1. However, a large vignetting occurs here. Large vignetting values also occur naturally in the case of multiple reflections in the lens body (see, for example, US 5 930 055 B1). SUMMARY

[0037] It is an object of the application in this context to provide an advantageous optical assembly. It is a further object to provide an advantageous objective, an advantageous image acquisition device, an advantageous image reproduction device, and an advantageous mobile device. These objects are achieved by the optical assembly according to the following, by the objective according to the following, by the image acquisition device according to the following, by the image reproduction device according to the following, and by the device according to the following. Further advantageous design options of the application are contained in the following.

[0038] The optical assembly according to the application comprises a central axis, which can coincide with the optical axis, an object side, an image side and a catadioptric assembly, wherein the catadioptric assembly comprises a first mirror having converging refractive power and a subsequent mirror having diverging refractive power. The optical assembly has a structural space or total length L of at most 25 millimetres (25 mm), preferably at most 10 millimetres (10 mm), along the central axis from the object side to the image side. The optical assembly also has a linear obscuration of at most 60%.

[0039] For applications as photographic objective (with collimated input end), the focal length can preferably be between 15 mm and 30 mm, for example 20 mm or about 20 mm. For applications in mobile devices, for example smartphones, the structural space or total length can be at most 9 mm, advantageously at most 6.5 mm. In the case of a microscope construction, i.e. applications as a microscope, the object distance from the optics (working distance FWD) can be at least 15 mm.

[0040] The optical assembly according to the application is advantageous in that it enables high-quality microscopic imaging with small obscuration in a small structural space.

[0041] In a first variant, the catadioptric assembly comprises a first optically partial mirror-coated optical member having a front side arranged on the object side and a back side arranged on the image side, and a second optically partial mirror-coated optical member having a front side arranged on the object side and a back side arranged on the image side, which optical members are arranged in the beam path in succession, in particular front-to-back, along the central axis, so that the first optical member is arranged on the image side of the second optical member. The first optical member, preferably the back side of the first optical member, comprises a radially inner region and a radially outer region with respect to the central axis, wherein the inner region is configured to be at least partially transmissive or transparent for object-side incident light, and the outer region is configured to be reflective on the back side for object-side incident light. The second optical member comprises a radially inner region and a radially outer region with respect to the central axis, wherein the outer region is configured to be transmissive or transparent for object-side incident light, and the inner region is configured to be reflective for image-side incident light. Here, the front side or the back side of the second optical member can have a reflective surface region. Furthermore, in this variant, at least a first refractive surface with refractive power, i.e. having refractive power, and a second refractive surface with refractive power, i.e. having refractive power, are arranged in the beam path between the back side of the first optical member and the front side of the second optical member.

[0042] For example, the front side of the first optical component and the front side and / or the back side of the second optical component are configured to be transparent. The areas of the respective reflective configuration can be configured circular or annular. The locally mirror-coated area of the first optical component can be designed concave on the object side. The locally mirror-coated area of the second optical component can be designed convex on the image side.

[0043] The described first variant of the application has the advantage that no further, i.e. easily light-transmissive, refractive optical element is required in the beam path behind the catadioptric assembly. A refractive element is not to be understood here as a plane-parallel plate, for example a protective window in front of the image receiver. A refractive surface arranged between the first optical component and the second optical component or constituted by the surfaces of the first optical component and the second optical component facing each other can correct the aberrations effectively in a space-saving manner. Furthermore, the described design has a significantly simpler construction in terms of installation technology compared to the prior art, so that production costs can be reduced at the same time.

[0044] In the exemplary design, the first refractive surface with refractive power can be constituted by the front side of the first optical component and / or the second refractive surface with refractive power can be constituted by the back side of the second optical component. The mentioned surfaces can be configured as aspherical or freeform surfaces and thus be designed for targeted correction of aberrations. An aspherical surface is understood to be a lens with a rotationally symmetrical surface, which can have surface regions with different radii of curvature from each other.

[0045] The first optical component can be configured to have refractive power, i.e. be refractive, only on the front side and / or only on the back side, and the image plane is arranged directly on the image side of the first optical component, so that no further, light-transmissive, optically effective surface, in particular refractive or diffractive, is arranged in the beam path. In other words, the optical assembly can be designed for arranging the image receiver or image acquisition device directly behind the back side of the first optical component in the beam path.

[0046] Optionally, at least one third optical component is arranged between the first optical component and the second optical component in geometric terms and in the beam path. The at least one third optical component is preferably configured to be refractive. The at least one third optical component can be designed for correcting at least one aberration. The imaging quality is further improved thereby.

[0047] It is advantageous, in particular in terms of installation technology, that the radial extension of the individual optical components of the optical assembly, i.e. the first optical component and / or the second optical component and / or the third optical component, differ from each other by a maximum of 2 mm or a maximum of 30%.

[0048] The outer region and the inner region of the back face of the first optical component can have different surface shapes from one another. In addition thereto or instead thereof, the outer region and the inner region of the front face and / or of the back face of the second optical component can have different surface shapes from one another. This offers numerous advantages in terms of more degrees of freedom of operation. Here, the outer region or the inner region of the back face or of the front face is predetermined by the above-mentioned inner region or outer region of the respective component.

[0049] The optical components mentioned can be configured rotationally symmetrical about a central axis. Between at least two of the optical components mentioned, an air lens, i.e. a gap filled with air, can be arranged. The extension dimension of the entrance pupil can be between 7 mm and 9 mm, for example 8 mm. At least one of the optical components mentioned can have at least one aspherical surface or a free-form surface. At least two of these optical components can be made of the same material, whereby the manufacturing costs can be reduced. The at least one region configured to be reflective can be configured as a condenser-type Mangin mirror.

[0050] In a second variant of the application, at least one field lens, for example a refractive field lens, is arranged in the beam path and / or geometrically between the catadioptric assembly and the image side, i.e. between the back face of the first optical component and the image plane. For the purposes of the present application, a field lens is understood to be a lens which is arranged at a position in the optical beam path at which the imaged chief ray height is greater than or equal to the marginal ray height. In particular, a field lens group can be arranged in the beam path and / or geometrically between the catadioptric assembly and the image side. The at least one field lens can be designed as a converging lens, i.e. a lens having a positive refractive power, and / or as a diverging lens, i.e. a lens having a negative refractive power. For example, there can be only one converging lens or only one diverging lens as a field lens. This facilitates a simple and compact construction of the optical assembly and can achieve a converging chief ray for correct volumetric imaging. In the case of a field lens group, the field lens group can comprise at least one converging lens and / or at least one diverging lens.

[0051] For example, at least one, for example refractive, field lens group, which comprises at least one lens or lens group with positive refractive power and / or at least one lens or lens group with negative refractive power, can be arranged in the beam path and / or geometrically between the catadioptric assembly and the image side of the optical assembly, i.e. between the back of the first optical member and the image plane. Thereby, a large degree of freedom for aberration correction and in particular for improving the quality of microscopic imaging is achieved. Advantageously, the field lens group comprises a first lens or lens group with positive refractive power and a second lens or lens group with negative refractive power, which is arranged in front of the first lens or lens group in the beam path, i.e. on the object side of the first lens or lens group. Thereby, conditions for volumetric imaging can be achieved, in particular by arranging a stronger positive refractive power on the image side behind a main beam which is very strongly divergent, the exit pupil is placed behind the image plane. The value of the geometric main beam angle can in particular be substantially the same as the optical or central axis in the object space and the image space. Here, the value of the main beam angle in the object space and the image space can differ by a maximum of 5 degrees.

[0052] As an alternative, the catadioptric assembly comprises a front side arranged on the object side, a back side arranged on the image side and a radially inner region and a radially outer region with respect to the central axis, wherein the inner region on the back side is configured to be at least partially transmissive or transparent for light rays incident from the object side and has a negative refractive power. This has the advantage that the inner region of the back side is configured as a lens and can act as a lens and the corresponding function of a field lens can be integrated into the catadioptric assembly, which in turn reduces the installation space.

[0053] The catadioptric assembly can for example comprise a first optically locally mirror-coated optical member with a front side arranged on the object side and a back side arranged on the image side and a second optically locally mirror-coated optical member with a front side arranged on the object side and a back side arranged on the image side, which are arranged in the beam path one after the other, in particular successively front and back, along the central axis, so that the first optical member is arranged on the image side of the second optical member. Here, the first optical member, preferably the back side of the first optical member, can comprise a radially inner region and a radially outer region with respect to the central axis, wherein the inner region is configured to be at least partially transmissive or transparent for light rays incident from the object side and the outer region is configured to be reflective on the back side for light rays incident from the object side. Here, the second optical member, for example the front side or the back side, comprises a radially inner region and a radially outer region with respect to the central axis, wherein the outer region is configured to be transmissive or transparent for light rays incident from the object side and the inner region is configured to be reflective for light rays incident from the image side. Here, the front side or the back side or the surface inside the member can be designed to be reflective. Advantageously, the radially inner region of the first optical member has a negative refractive power. This has the advantages mentioned in the above paragraphs.

[0054] Preferably, the optical assembly is configured asymmetrically with respect to a plane arranged perpendicular to the central axis. As opposed to symmetrical assemblies, asymmetric assemblies have the advantage of achieving the smallest possible construction space. In another preferred design, which is particularly efficient in terms of construction space, the optical assembly does not produce a real intermediate image or an even number of intermediate images between the object side and the image side (or between the object plane and the image plane). Thereby, a negative imaging ratio can be produced.

[0055] In a third variant of the application, a field lens group, preferably a refractive field lens group, is arranged on the image side of the catadioptric assembly. The optical assembly defines an image plane. Furthermore, the optical assembly has a construction length L s measured from the vertex of the first optical surface (e.g. the front face of the catadioptric assembly or the second optical member) to the image plane FL and the field lens group has a paraxial focal length f' FL <0), wherein the value of the paraxial focal length f' FL is smaller than the construction length L s (|f' FL | < L s ). The third variant has the advantage of a significantly reduced vignetting, in particular.

[0056] The reason for the vignetting is in principle that the convex secondary mirror is usually arranged in front of the concave primary mirror of the catadioptric assembly in a geometric sense, thus blocking the primary mirror. As already discussed above, a first rough estimate of the value of the vignetting thus lies in the ratio of the outer diameters of the two reflecting surfaces. If there are no other optical elements between the two reflecting mirrors or the regions of the reflecting configuration and the field angle is close to zero, this estimate will give the true vignetting.

[0057] The optics between the mirrors can have a favorable influence on the vignetting. A limited field angle increases the vignetting. For the specific design of the vignetting, two points are decisive. At the secondary mirror, which is close to the object in a geometric sense, the light beam incident into the optical assembly is cut off by the contour of the secondary mirror, mainly by the inner region of the reflecting configuration of the second optical member. At the primary mirror, which is close to the image in a geometric sense, mainly at the outer region of the reflecting configuration of the first optical member, the reflected light beam is cut off by the central region or the radially inner region used to derive the light rays reflected by the secondary mirror.

[0058] In order to keep the vignetting as small as possible, the diameter of the secondary mirror should be minimal and the diameter of the inner region of the transmissive configuration of the primary mirror should be minimal. First, the second condition schematically shown in Figure 3 is considered. It is assumed that the light beam path is rotated from the object lens and follows the light beam from the detector back through the optical system. If it is assumed that there is a detector for telecentric illumination (see Figure 3If the central hole or radially inner region of the primary mirror has a size of at least the size of the detector diagonal plus the beam diameter increased by the beam divergence, the beam diameter d0in front of the detector or image plane 6 increases sharply with distance. If the primary mirror is located in front of the image plane 6 at a distance L0, the central hole or radially inner region has at least the size of the detector diagonal plus the beam diameter increased by the beam divergence.

[0059] If the telecentricity at the detector is deviated such that the chief beam at the detector diverges in front of the optical axis (see Figure 3 lower left), i.e. the exit pupil is located close in front of the image plane 6, the beam diameter d1may thus be designed significantly smaller over the height of the central hole or radially inner region of the first mirror (again assuming a distance L0in front of the detector). However, catadioptric structures require the system pupil to be located in the catadioptric part of the system. Thus, the pupil position has to be located away from the image plane, although there is a case of a favorable strong anatelmaticity at the image. A solution to this is to use a field lens group with strong negative refractive power, as for example Figure 3 is shown schematically on the right. A field lens is understood here as a lens which is arranged near the detector and which is characterized, for example, in that the chief beam height is greater than the marginal beam height.

[0060] Due to the use of a field lens with negative refractive power, the diameter of the beam is minimized over the height of the central opening or radially inner region of the first mirror, which is advantageous for the vignetting of the entire system. However, it must be noted that the strong negative refractive power near the image plane contributes to the Petzval sum and provides an overcorrection of the system. The converging mirror which is required for imaging likewise contributes to the Petzval sum and provides an overcorrection. The single element which contributes significantly and overcorrects the Petzval sum is the convex secondary mirror. Thus, in order to achieve a balanced Petzval sum, the curvature of the secondary mirror has to be increased. This in turn leads to the fact that the marginal beam height at the position of the secondary mirror has to be smaller, so that the increased curvature does not have an excessively large effect on the total refractive power of the system. The total refractive power of an optical system or optical assembly is given by the sum of the products of the refractive power of the individual surfaces and the relative marginal beam height. The relative marginal beam height is understood here as the quotient of the marginal beam height and the entrance pupil radius. The above conditions force the secondary mirror to be scaled down and the vignetting to be reduced. In summary, in order to reduce the vignetting, a strong negative refractive power has to be used in the field lens group between the catadioptric assembly and the image plane or image side of the optical assembly. Preferably, the paraxial focal length f' FL has a value which is smaller than the structure length L s (|f' FL | < L s ).

[0061] In order to give the refractive power mathematically, the classical paraxial refractive power or the refractive power based on the envelope radius can be used. The classical refractive power of a thin lens in air is

[0062]

[0063] Given by the vertex radii r1, r2 of the lens and the refractive index or refractive index n of the lens medium as

[0064]

[0065] Here, f' is the image-side focal length of the lens. In the field of mobile phone optics, very strongly aspherical optical elements are used, so that the paraxial refractive force usually only has a very limited explanatory power for the real effect of the optical element. It is very common that the aspherical surface is formed so strongly that the optical element has a different refractive force in the radially inner region than in the radially outer region. These optical elements are designed to be converging, for example, near the optical or central axis, i.e. in the radially inner region, but diverging in the edge region or radially outer region. In order to express the requirement for the diverging effect of the main beam in the edge region or radially outer region of the field lens, the envelope radius- refractive force should therefore be defined. This envelope radius- refractive force is based on the envelope radius of the surface that delimits the respective surface.

[0066] p is the sag of the lens surface in the maximum optical free height h of the lens Max , i.e. the sag measured perpendicular to the central axis of the lens. A circle can then be determined which intersects the lens surface at the vertex and at the height h Max . This circle has a radius

[0067]

[0068] r bf is now defined as the envelope radius (English: Best Fit Radius). The envelope radius- refractive force

[0069]

[0070] Here, r hr,1 and r hr,2 are the respective envelope radii of the front and back surface.

[0071] On the image side of the catadioptric assembly there can be arranged at least one field lens, preferably configured refractively, for example a field lens group, and the optical assembly can define an image plane. The optical assembly can have a free optical diameter D2 on the image side of the back face of the catadioptric assembly, in particular of the first optical member of the catadioptric assembly. Here, the free optical diameter is understood to be the maximum beam height (i.e. the distance from the optical or central axis) of the light beam used to image on this surface. The image plane defined by the optical assembly can have an imaging plane with a diameter D1. The imaging plane here defines the region of the image plane in which an image can be produced by the optical assembly. The optical assembly can also have an image receiver with a diameter D1. Here, the ratio of the free optical diameter D2 to the diameter D1 of the imaging surface or image receiver is less than 1 (D2 / D1). Thus, the beam path is widened by the field lens or field lens group and thus the vignetting is reduced.

[0072] Furthermore, on the image side of the catadioptric assembly there can be arranged at least one field lens, preferably configured refractively, for example a field lens group, and the optical assembly can define an image plane, wherein the optical assembly has a focal length f' and a construction length L s measured from the vertex of the first optical surface, for example the front face of the catadioptric assembly or the second optical member, to the image plane. s The ratio of the focal length f' to the construction length L s is greater than 2 (f' / L > 2). Thereby, microscopic imaging can be achieved with optical means designed for mobile devices, for example mobile phones.

[0073] Furthermore, on the image side of the catadioptric assembly there can be arranged at least one field lens, preferably configured refractively, for example a field lens group, and the optical assembly can define an image plane. Here, the optical assembly has an imaging ratio β, a distance FWD of the object plane, in particular the object surface, from the vertex of the first optical surface, for example the front face of the catadioptric assembly or the front face of the second optical member, measured along the central axis of the optical assembly, and a construction length L s measured from the vertex of the first optical surface to the image plane. The product of the imaging ratio β and the quotient of the distance FWD and the construction length L s is greater than 2.

[0074]

[0075] This design also enables microscopic imaging in the case where only very little construction space is available for the corresponding optical means.

[0076] Optionally, the chief ray angle of the beam path can have a directional cosine rvl2on the back side of the catadioptric assembly immediately before exiting the catadioptric assembly, which has a refractive index n2on the back side, and the chief ray angle of the beam path can have a directional cosine rvl1in the image-side medium with a refractive index nl in the image plane, e.g. on the detector, where

[0077]

[0078] By this design solution the vignetting is effectively reduced.

[0079] The geometric angle of the chief ray to the optical axis can have a first value in the object space, and the geometric angle of the chief ray to the optical axis can have a second value in the image space, which second value differs from the first value by less than 1 degree. Thereby, real volume imaging can be achieved with reduced vignetting.

[0080] In all of the above variants, the assembly can have a negative imaging ratio and / or a positive entrance pupil location and / or a positive exit pupil location. The front side of the second optical member can have a concave shape near the edge. As a result of the negative imaging ratio and advantageously, no intermediate image is generated. The entrance pupil location is preferably close to 0, as the system stop is either located at the first surface, however at the latest on the "first optical element". If the chief ray intersects the optical axis behind the image plane, the location of the exit pupil is positive, which is pursued according to the present application.

[0081] The number of reflections or refractions of the beam path can be even. In order to effectively reduce the construction space, the optical assembly is not symmetrically configured with respect to any plane perpendicular to the central axis. Thus, the construction is asymmetric in this respect.

[0082] The optical assembly can have an aperture stop, and the geometric distance between the object plane defined by the optical assembly and the aperture stop is preferably greater than the distance between the aperture stop and the image plane defined by the optical assembly.

[0083] Preferably, at least one, advantageously two or more or all of the optical surfaces or optically effective surfaces, or all but one, or all but two, of the optical surfaces or optically effective surfaces, are configured to be continuous and at least once continuously differentiable in the beam path. The respective surfaces can in particular have a uniform polynomial surface description over the entire surface. This is in particular advantageous in terms of manufacturing technology, however also provides sufficient degrees of freedom to reduce aberrations.

[0084] The optical assembly advantageously has a linear vignetting of less than 50%, e.g. less than 40%. The vignetting can for example be between 30% and 50%.

[0085] The optical assembly according to the application can be designed as a microscope, in particular with an imaging ratio between 2 and 0.25 (2 > | β' | > 0.25). The optical assembly according to the application can for example be designed for mobile devices (smartphones, notebooks, netbooks, tablets, smartwatches, etc.).

[0086] At least one optical member of the optical assembly according to the application can have at least one aspherical surface or a free-form surface. Furthermore, only one optical member in the optical assembly can be made of chert-like material. At least two of the optical members can also be made of the same material or a material different from each other (for example of a crown material or a chert material). The at least one region configured to be reflective can be configured as a light-collecting Mangin mirror.

[0087] The objective according to the application comprises the above-mentioned optical assembly according to the application. The objective has the features and advantages already mentioned in connection with the optical assembly according to the application. The objective can be configured as a camera objective or a microscope objective for imaging objects at a distance.

[0088] The image acquisition device according to the application (for example a camera or a microscope) and the image reproduction device according to the application (for example a projector) comprise the objective according to the application.

[0089] The device according to the application (which can be a microscope or a mobile device) comprises the image acquisition device according to the application or the image reproduction device according to the application or the optical assembly according to the application. The mobile device according to the application can be a mobile phone, a tablet, a notebook, a smartwatch, a netbook, etc. It has the advantages already described for the optical assembly according to the application. BRIEF DESCRIPTION OF DRAWINGS

[0090] The application will be explained in detail below with the help of embodiments and with reference to the drawings. Although the application is further illustrated and described in detail by preferred embodiments, the application is not limited to the disclosed examples and other variants can be derived therefrom by a person skilled in the art without departing from the scope of protection of the application.

[0091] The drawings are not necessarily very detailed and to scale and can be shown enlarged and reduced in order to provide a better perspective. The functional details disclosed herein should therefore not be understood as limiting, but merely as illustrative in order to provide a person skilled in the art with a basis for guidance in order to use the application in various ways.

[0092] The expression "and / or", as used herein when used in a list of items, indicates that one or more of the items can be used and, optionally, also one or more of the other items in the list of items can be used. For example, when describing a composition containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C.

[0093] Figure 1 A light beam path for producing real volume imaging is schematically illustrated.

[0094] Figure 2 A light beam path through a catadioptric assembly is schematically illustrated to illustrate vignetting.

[0095] Figure 3 Options for reducing vignetting are schematically illustrated.

[0096] Figure 4 A first embodiment of an optical assembly according to the application is schematically illustrated.

[0097] Figure 5 A second embodiment of an optical assembly according to the application is schematically illustrated.

[0098] Figure 6 A third embodiment of an optical assembly according to the application is schematically illustrated.

[0099] Figure 7 A fourth embodiment of an optical assembly according to the application is schematically illustrated.

[0100] Figure 8 A fifth embodiment of an optical assembly according to the application is schematically illustrated.

[0101] Figure 9 A sixth embodiment of an optical assembly according to the application is schematically illustrated.

[0102] Figure 10 A seventh embodiment of an optical assembly according to the application is schematically illustrated.

[0103] Figure 11 An eighth embodiment of an optical assembly according to the application is schematically illustrated.

[0104] Figure 12 A ninth embodiment of an optical assembly according to the application is schematically illustrated.

[0105] Figure 13 A tenth embodiment of an optical assembly according to the application is schematically illustrated.

[0106] Figure 14 schematically shows a thirteenth embodiment of an optical assembly according to the application.

[0107] Figure 15 schematically shows a twelfth embodiment of an optical assembly according to the application.

[0108] Figure 16 schematically shows a thirteenth embodiment of an optical assembly according to the application.

[0109] Figure 17 schematically shows a fourteenth embodiment of an optical assembly according to the application.

[0110] Figure 18 schematically shows a fifteenth embodiment of an optical assembly according to the application.

[0111] Figure 19 schematically shows a device according to the application. DETAILED DESCRIPTION

[0112] Figure 1 The optical beam path 17 for generating real volumetric imaging is schematically shown and has been described in the introduction of the above description. The first converging lens 7 generates the images A0' and A1' from the objects A0 and A1, however these images do not correspond to each other in size proportion as Figure 1 is shown above. In Figure 1 below, the direction of the main beam 9 is adapted by means of a further field lens in the form of a second converging lens 8, so that the size proportion of the generated images A0' and A1' corresponds to each other in size proportion to the objects A0 and A1. The central axis of the lenses 7 and 8, which coincides with the optical axis, is marked with the reference numeral 2.

[0113] Figure 2 The optical beam path through a catadioptric assembly is schematically shown, which comprises a first reflective optical surface 31 (primary mirror) and a second reflective optical surface 32 (secondary mirror) in a radially outer region, and the calculation of the obscuration has been described above. The entrance pupil or stop is marked with the reference numeral 18. The light rays, which are incident from the left in the figure, are first reflected by the first reflective optical surface 31, wherein a portion of the light rays is obscured by the second reflective optical surface 32. Subsequently, the light rays reflected by the first reflective optical surface 31 are reflected by the second reflective optical surface 32 and pass through the first optical surface 31 in a radially inner region. In Figure 2 below, the directional cosine of the marginal beam R0 is marked with the arrow rvl o and the directional cosine of the beam R1 is marked with the arrow rvl1.

[0114] The above described Figure 3Options for reducing the degree of shading are shown. Here, the image plane or detector is marked with reference 6, and a diverging lens for widening the beam path 17 is marked with reference 27.

[0115] The first embodiment variant of the application is explained in detail below with the aid of the embodiment shown schematically in Figures 4 to 9 The optical assembly 1 shown comprises a central axis 2, which coincides with the optical axis in the example shown, an object side 3 and an image side 4. Here, the object side 3 is directed towards an object or object plane 5 to be imaged, while the image side 4 is directed towards an image plane 6 or a detector, for example a camera, arranged in the region of the image plane. The optical assembly 1 also comprises a catadioptric assembly 10.

[0116] The catadioptric assembly 10 comprises a first partially mirror-coated optical member 11 and a second partially mirror-coated optical member 12. These optical members are configured as lenses in the example shown. The first partially mirror-coated optical member 11 comprises a front face 13 and a back face 14. The second partially mirror-coated optical member 12 likewise comprises a front face 15 and a back face 16. Here, the front faces 13 and 15 are directed in the direction of the object side 3, while the back faces 14 and 16 are directed in the direction of the image side 4. The first optical member 11 and the second optical member 12 are arranged in the beam path 17 in succession along the central axis 2, such that the first optical member 11 is arranged on the image side of the second optical member 12.

[0117] The first optical member 11 comprises a radially inner region 21 and a radially outer region 22 with respect to the central axis 2. Here, the inner region 21 is configured to be at least partially transparent or transmissive for object-side incident light. The outer region 22 is configured to be reflective for object-side incident light. To this end, the back face 14 of the first optical member 11 has a mirror coating 23. This mirror coating is configured to be concave (convex on the image side) on the object side in the example shown.

[0118] The second optical member 12 comprises a radially inner region 24 and a radially outer region 25 with respect to the central axis 2. Here, the outer region 25 is configured to be transparent or transmissive for object-side incident light. The inner region 24 is configured to be at least partially transparent or transmissive for object-side incident light and reflective for image-side incident light. To this end, the front face 15 of the second optical member 12 has a mirror coating 26. This mirror coating is configured to be convex on the image side (concave on the object side) in the example shown.

[0119] A plane-parallel plate 28 is arranged between the back face 14 of the first optical member 11 and the image plane 6. Here, this plate can be a transparent protective layer.

[0120] The present embodiment is a microscope objective with an imaging ratio of -1 :0.8, which has a very large working distance of 28 mm at a total construction length of 8.5 mm. The system has a front stop, i.e. the system stop 18 is located in front of the actual optical system. The stop 18 can also be located inside the optical assembly 1. The decisive factor for the stop location is that a mechanically variable stop can be easily realized mechanically if necessary. The stop 18 can also be located, for example, between the two optical members 11 and 12.

[0121] The optical members 11 and 12 shown can be configured, for example, to be rotationally symmetrical. In the example shown, the light rays are incident into the optical assembly 1 through a very large entrance pupil with a diameter of approximately 8 mm and are refracted through the front face 15 and the back face 16 of the second optical member 12 in its radially outer region 25. The front face 15 and the back face 16 of the second optical member 12 and the front face 13 of the first optical member 11 can be designed as aspherical. For the incident light rays, the mirror coating 23 of the first optical member 11 acts as a collecting type Mangin mirror, which reflects the light back again to the second optical member 12. For the incident light rays, the mirror coating 26 of the second optical member 12 acts as a diverging type Mangin mirror, which reflects the light back again to the first optical member 11. Finally, the light rays re-pass the first optical member 11 near the axial region, where this first optical member acts as a transmissive lens in the inner region 21. Subsequently, no further optical element with refractive power can be passed through and the light rays hit the image plane 6.

[0122] The front face 15 of the second optical member 12 has a different surface shape at the transition between the outer region 25 and the inner region 24, i.e. between the transmissive region and the reflective region, than in the regions mentioned. Although the transition is continuous, it is not differentiable, i.e. the transition has a cusp. This cusp can be rounded off in the installation technology by means of a phase in a mechanical manner. The transition can also be designed to be non-continuous.

[0123] Figure 4 The optical assembly 1 shown in the middle has a linear obscuration of 40%. Linear obscuration means that in the entrance pupil, the inner 40% of the entrance pupil coordinates cannot pass through the optical assembly or cannot be used for imaging. This is equivalent to a linear obscuration of 16% (= 40% of 40%) in the entrance pupil area. 2 or 0.4 2 ).

[0124] A vignetting mainly occurs on the front side 15 of the second optical component 12 when light is incident into the optical assembly 1. Here, the light beams in the inner region of the pupil 18 are blocked at the mirror coating 26. Further vignetting can occur when the reflection on the back side 14 of the first optical component 11, i.e. when the incident light beams pass through the central region, i.e. the inner region 21, which is not mirror-coated, and are not reflected back to the second optical component 12.

[0125] The front side 13 of the first optical component 11 and / or the back side 16 of the second optical component 12 are designed for correcting aberrations. They can be designed as spherical or as aspherical or as freeform surfaces, in particular. In the example shown, all the surfaces and surface regions of the first optical component 11 and of the second optical component 12 shown are configured as aspherical surfaces.

[0126] In principle, the first optical component 11 and the second optical component 12 are made of different optical materials. In the example shown, the second optical component 12 has a refractive index of 1.493 and an Abbe number of 51.3 and is used as a crown material here. The first optical component 11 has a refractive index of 1.589 and an Abbe number of 26.2 and is used as a flint material here.

[0127] The first optical component 11 and the second optical component 12 have comparable diameters. The diameters can be identical or can differ from one another by a maximum of 30%.

[0128] Figure 5 The example shown is very similar to the example shown in Figure 4 The main difference is that no second optical material is used here. The first optical component 11 and the second optical component 12 are both made of a crown material. In other words, it is a single material system. Instead, the first optical component 11 and the second optical component 12 can be made of or comprise a flint-like material.

[0129] Figure 6 The example shown shows the design principle of a conventional photographic objective described in the previous examples, i.e. the design principle from an infinite object distance to the image receiver. This involves an optical assembly 1 configured as an objective which has a focal length of f' = 22 mm in a construction space of only L S = 8.5 m measured along the central axis 2. The telephoto factor is thus F = 0.39 from a purely calculative point of view. Further, a single material system is involved. The vignetting of the optical assembly 1 is 40% in this example.

[0130] Optical assembly 1 also includes a third optical element 19, arranged geometrically or spatially between the first optical element 11 and the second optical element 12 in the beam path 17. The third optical element 19 is passed through three times in the beam path 17 and is configured as a refractive lens. The third optical element has a front surface 29 and a back surface 30. The front surface 29 and back surface 30 of the third optical element 19 can be designed as spherical or aspherical, or as freeform surfaces.

[0131] exist Figure 7 In the illustrated embodiment, an optical component 1 in the form of a microscope objective is shown, which has the optical characteristics of the first embodiment. In this example, the specular coating 26 of the second optical component 12 is disposed on the back surface 16, i.e., on the image-facing side. The specular coating 26 is configured to be convex on the image side. The specular coating has a uniform, generally arbitrarily continuously differentiable shape, i.e., a uniform polynomial surface description on the entire surface of the back surface 16 of the second optical component 12. Similar to the third embodiment, a third optical component 19 in the form of a lens through which light passes three times in the beam path 17 is geometrically disposed between the first optical component 11 and the second optical component 12 in the beam path 17.

[0132] Unlike the previously described embodiment where the front surface 15 of the second optical component 12 cannot be continuously differentiated, in this embodiment and the following two embodiments, the shading degree is 50%. A uniform (i.e., continuous and differentiable) surface design facilitates surface fabrication and reduces production costs. This surface design is also advantageous in terms of centering the corresponding optical components and precisely positioning the mirror-coated sub-regions.

[0133] Figure 8 The fifth embodiment shown is the same as Figure 7 The difference in the fourth embodiment shown is that the front surface 29 of the third optical element 19 is abutted against the back surface 16 of the second optical element 12. Furthermore, the second optical element 12 is constructed as a lens that can be easily passed through. Another structural difference is that the second reflection does not occur on the (convex) back surface of the second optical element 12, but rather on the (concave) front surface of the third optical element 19. Therefore, in this embodiment, the catadioptric assembly is formally composed of the first optical element 11 and the third optical element 19.

[0134] exist Figure 9 In the sixth embodiment shown, the principles of the invention are further applied to an optical component 1, which is constructed as a photographic objective and has a collimated beam input. A mirror coating 26 is then disposed on the back surface 16 of the second optical component 12. The third optical component 19 is designed as a lens through which light passes three times.

[0135] The following is based on Figures 10 to 13The second embodiment variant of the application is explained in detail with reference to the embodiment shown in the figures.

[0136] In Figure 10 In the design shown, the catadioptric assembly 10 is designed as a single catadioptric component. This catadioptric component has a front face 33 arranged on the object side and a back face 34 arranged on the image side. The front face 33 comprises a radially inner region 35 which is configured to be reflective for image-side incident light and a radially outer region 36 which is configured to be transmissive. The back face 34 has a radially inner region 37 which is configured to be transmissive for object-side incident light and a radially outer region 38 which is configured to be reflective for object-side incident light. In this case, the mirror-coated regions of the front face 33 are concavely shaped, i.e. convexly in the beam path 17 or on the image side, as viewed from the outside, while the mirror-coated regions of the back face 34 are convexly shaped, i.e. concavely in the beam path, as viewed from the outside.

[0137] In geometric or spatial terms and in the beam path 17, a field lens group 40 and optionally a plane-parallel plate 28 are arranged between the back face 34 of the catadioptric assembly or the catadioptric component 10 and the image plane 6, wherein the plane-parallel plate 28 is arranged on the image side of the field lens group 40. The field lens group 40 comprises a lens unit with negative refractive power, here consisting of three refractive diverging lenses 40, 41 and 43, and a lens unit with positive refractive power, here consisting of a refractive converging lens 44.

[0138] The front face 33 of the catadioptric assembly 10 generally does not have a uniform surface shape. The mirror-coated radially inner region 35 is generally described by a different curvature equation than the transmissive radially outer region 36. Preferably, both curvatures are at least configured such that they continuously adjoin one another. This does not necessarily have to apply to the back face 34, however, it can also apply to this back face.

[0139] The basic course of the beam path 17, in particular within the catadioptric component 10, generally corresponds to that described in connection with the already explained embodiments. For the case that the light rays emanate from the radially inner region 37 of the back face 34, there is a real intermediate image behind the back face 34 if the field lens group 40 is not present. For the case that the light rays emanate from the catadioptric component 10, the main beam diverges from the optical axis 2, i.e. the pupil of the air space behind the back face 34 is virtual and located in front of the back face 34.

[0140] The field lens group 40 constitutes a clear catadioptric structure with positive and negative refractive power. The light rays exit the catadioptric member or catadioptric assembly 10 with converging marginal ray angles, i.e. a real intermediate image is generated a short distance behind the catadioptric assembly 10 as already mentioned. On the other hand, the intersection of the chief ray with the optical axis 2 is located in front of the catadioptric assembly 10 when exiting it, i.e. the chief ray is diverging. In order to make the chief ray converge, a positive refractive power has to be used on the image side of the catadioptric assembly 10 at a position where the chief ray height is greater than the image size. This is only the case at a certain distance behind the catadioptric assembly 10, however, where the marginal rays have already reached the focal points at this position.

[0141] In order to shift the focal points of the marginal rays further in the direction of the image plane 6 from the catadioptric assembly 10 and to make the chief ray height rise more quickly in the direction of the light rays, a strongly diverging refractive power is used directly behind the catadioptric assembly 10, i.e. on the image side, in particular in the form of a lens unit consisting of the diverging lenses 41, 42 and 43 with negative refractive power, which makes the intermediate image significantly further away from the catadioptric assembly 10 so that a desired converging chief ray angle can subsequently be set using the lens 44 or a corresponding lens group with positive refractive power.

[0142] In the embodiment shown, the lens unit acting as a diverging lens is the three double aspherical lenses 41, 42 and 43 and the lens unit acting as a converging lens is the converging double aspherical lens 44.

[0143] The imaging ratio of the optical assembly shown is -1:1, which can be an objective. The angle of the chief ray is identical in value and only in sign in the object space and the image space.

[0144] In the embodiment shown, the imaging ratio of the optical assembly shown is -1:1, which can be an objective. The angle of the chief ray is identical in value and only in sign in the object space and the image space. Figure 11 The embodiment shown differs from the embodiment shown in Figure 10 The embodiment shown differs from the embodiment shown in

[0145] Figure 12 The embodiment shown is associated with the embodiment shown in Figure 10 The catadioptric assembly 10 here comprises a first optical member 11 and a second optical member 12, which is similar to the embodiment of the first embodiment variant. The advantage of this design is that additional lens surfaces in the form of the back surface 16 of the second optical member 12 and the front surface 13 of the first optical member 11 are provided for use as optical design elements, in particular for beam shaping and correction of aberrations.

[0146] Furthermore, both the first optical component 11 and the second optical component 12 have at least one surface which has a non-uniform curvature description. For example, the radially outer region of the front face 15 of the second optical component 12 is designed to be strongly aspherical, while the radially inner region of the front face 15 of the second optical component 12 is designed to be strongly concave as viewed from the outside. In the design shown, the back face 16 of the second optical component 12 is characterized by a uniform curvature description.

[0147] The first optical component 11 has a weak meniscus configuration in the radially outer region 22, while the radially inner region 21 has a strong meniscus shape, i.e. a shape which is strongly convex as viewed from the outside. Figure 10 The lens unit which assumes the function of a diverging lens in the embodiment shown. In this example, the field lens group 40 consists of a converging lens 44 or a corresponding converging lens group outside the catadioptric assembly 10. The advantage of this design is that a very simple and compact arrangement can be achieved overall, which requires only very few lens elements, among other things.

[0148] Figure 13 The embodiment shown differs from the embodiments described above in that it is designed for use in or with a water solution and thus has an imaging ratio of -1.334:1.

[0149] The third embodiment variant of the application is explained in detail below with the aid of the embodiment shown schematically in Figures 14 to 18 Here, the focus of the third embodiment variant is primarily on effectively reducing the vignetting.

[0150] Figure 14 The optical assembly 1 shown is designed as a photographic objective, i.e. for imaging objects located at a distance. The photographic objective or the corresponding optical assembly 1 shown has a focal length of 22 mm and is implemented in an axial installation space of not more than 6 mm. The telephoto factor is thus F = 3.67. Here, the axial installation space characterizes the distance from the front entry face, here, i.e. the front face 15 of the second optical component 12, to the image plane 6. In terms of this distance, two flat surfaces are considered between which the entire optical assembly 1 can be arranged. Thus, not only the distance of the front surface vertex from the image plane is considered, but also the entire entry surface.

[0151] The front face 15 of the second optical component 12, in turn, does not have a uniform curvature description. Both the radially outer region 25 and the radially inner region 24 have an aspherical shape on the front face 15. However, the aspherical equation for describing the radially outer region 25 of the front face 15 is different from the aspherical equation for describing the radially inner region 24 of the front face 15. However, the surfaces are designed such that the two regions at least continuously, but generally non-differentiable, adjoin one another. This design is advantageous in terms of manufacturing technology.

[0152] The curvature description of the back face 14 of the first optical member 11 is also not uniform. Seen from the outside, the radially outer region 22, which is configured to be reflective, is convex, i.e. the reflection from the inside of the first optical member 11 takes place on a surface which is hollow or concave in the direction of the light rays. The back face 14 is mainly concavely shaped in the radially inner region 21. The two partial curvature descriptions are aspherical and continuously, however non-differentiable, adjoin one another.

[0153] In the beam path 17, the catadioptric assembly 10 is connected to a lens group 40, which in this embodiment consists of a first diverging lens 41 of substantially low refractive power, for example made of polycarbonate, and a second diverging lens 42 of high refractive power. Here, the diverging lens 42 of high refractive power serves, inter alia, as a field lens with negative refractive power which is required for reducing the vignetting. The vignetting is 40% in the present case. In this embodiment, the focal length of the optical assembly 1 or objective has the value f' = 20 mm, i.e. the total refractive power is Furthermore, the field lens assembly 40 has a vertex refractive power of 522 dpt.

[0154] The illustrated optical structural elements and lenses are preferably mainly made of a crown material, for example PMMA (PMMA - Polymethyl methacrylate). The lens 41 is made of polycarbonate and has a bi-aspherical shape. The use of a low refractive power lens 41 made of flint material, such as polycarbonate, also balances the chromatic correction of the overall design.

[0155] The diameter of the radially inner region 24 of the second optical member 12 has a value which is slightly greater than the inner region 21 of the first optical member 11. Both diameters are significantly smaller than the image diagonal, i.e. smaller than the diameter of the image plane 6. To quantify, a (optically free) diameter ratio between the region 24 and the diameter of the image diagonal can be given, which is at least smaller than 0.9, in particular smaller than 0.8 or 0.7. For example in the case of a Figures 4 to 9 , the diameter ratio is approximately equal to 1. For Figure 14 the illustrated example, the diameter ratio is 0.61 ; for Figure 15 the illustrated example, the diameter ratio is 0.58; for Figure 16 the illustrated example, the diameter ratio is 0.63; for Figure 17 the illustrated example, the diameter ratio is 0.60; and for Figure 18 the illustrated example, the diameter ratio is 0.62. This again reflects the fact that the diverging field lens 41 or 42 or the field lens assembly 40 achieves a strong beam contraction and thus can achieve a minimum vignetting.

[0156] Furthermore, for a smaller light-blocking degree, the radially outer region 22 (i.e., the reflecting region) of the first optical element 11 has the largest possible diameter, thus maximizing the diameter ratio between the radially outer mirror-coated region 22 and the radially inner un-mirror-coated region 20. This, in turn, has a favorable effect on the light-blocking degree, thereby reducing it. The light-blocking degree is reduced in particular by the fact that the first optical surface hit by light (i.e., the front surface 15 of the second optical element 12) has a concave and therefore divergent shape in the edge region. This particularly increases the diameter of the light beam at the location of the first optical element 11 and thus facilitates the achievement of a smaller light-blocking degree.

[0157] and Figure 14 The embodiments shown are different, in Figure 15 The illustrated embodiment omits the first field lens 41. The effect of replacing lens 41 is achieved in the following way: the first optical element 11 is made of polycarbonate and the radially inner region 21 has a different surface description than the radially outer sub-region 22, thus the back surface 14 no longer has a uniform surface description. However, the surface descriptions of the radially inner and radially outer regions are continuously, although not continuously differentially, connected to each other on the back surface 14. In other respects, Figure 15 The illustrated embodiments and Figure 14 The examples shown correspond to those described.

[0158] Figure 14 and Figure 15 The embodiments shown relate to optical devices with an infinitely large input intercept, which are typically used, for example, in the field of photographic optics in mobile phones. Figures 16 to 18 The embodiments shown relate to projection lenses based on the same principle, namely, achieving a catadioptric assembly with the lowest possible light-blocking effect. Here, the imaging ratio is close to |β| = 1:1 to enable microscopic applications. Here, despite a very compact structure, a large working distance (FWD) should be achieved for 1:1 imaging. The working distance here should be the structural length L. s Or twice the quotient of the total length or structural space L and the imaging scale β:

[0159] Or when necessary

[0160] Here, L s The length of the structure is represented by L, which is the distance from the vertex of the first lens to the image plane. L represents the total length or structural space, which is the distance between two planes that can "push in" the entire optical device. In the current case, it is the distance from the lens edge to the image plane measured parallel to the optical axis.

[0161] In the case of the illustrated microscope objective, the imaging ratio is -0.8:1 and the overall length or construction space L is approximately 6.5 mm, i.e. the working distance should be at least 15 mm.

[0162] In the case of the embodiment illustrated in Figures 16 to 18 the working distance at the object is correspondingly 25 mm. With the imaging ratio of -0.8:1 and the construction space L of 6.5 mm already mentioned, the condition mentioned for the working distance FWD is well met. Furthermore, the individual optical components and lenses and their materials and Figure 16 The order of the surfaces of the embodiment illustrated in Figure 15 corresponds to the embodiment illustrated in Figure 15 Unlike the embodiment illustrated in

[0163] In the case of the embodiment illustrated in Figure 17 an optical assembly with an imaging ratio of -0.8:1 in the form of a microscope objective is illustrated. The overall construction is identical to the embodiment illustrated in Figure 15 Here too, the first of the two field lenses, i.e. the lens 41, is dispensed with and instead a first optical component 11 made of flint material, for example polycarbonate, is used and the back face 14 of the first optical component 11 is designed as a non-uniformly defined surface, such that the optical effect in the transmissive radially inner region 21 differs from the optical effect in the reflective radially outer region 22. Here too, the two sub-surface regions are continuous, however not differentiably adjoined to one another. The obscuration is in turn 36%.

[0164] In the case of the embodiment illustrated in Figure 18 the design freedom of the non-uniformly defined back face 14 of the first optical component 11 is dispensed with, so that the optical assembly 1 now consists of a catadioptric assembly 10 with a non-uniformly defined front face 15, a uniformly defined back face 14 and a field lens 42 with negative refractive power. The obscuration in this case is 38%.

[0165] The features of the embodiment of the third variant which are advantageous for a low obscuration are summarized in the following table. Here, L s characterizes the construction length, i.e. the distance of the first lens vertex from the image plane. L characterizes the overall length or construction space, i.e. the distance of two planes between which the entire optical device can be "pushed in", i.e. in the present case the distance of the lens edge measured parallel to the optical axis from the image plane. D2 is the optical free diameter of the transmissive region on the back face of the first optical component 11. D i is the diameter of the detector or its image diagonal or the diameter of the surface of the image plane or the exit pupil at which the image is generated. F FL ' is the paraxial refractive power of the field lens group with negative refractive power, RH1 and RH2 are the envelope radii of the field lenses with negative refractive power. F FLHRVL is the envelope radius - refractive power of the field lens with negative refractive power. N2 * RVL2 is the cosine of the meridional optical direction of the main beam before exiting from the first optical member 11. N i RVL i is the cosine of the optical direction of the main beam on the detector or image plane 6. Here, the cosine of the optical direction is understood as the cosine of the geometric direction multiplied by the refractive index of the respective medium considered.

[0166] Table 1:

[0167] Figure [[ L s ]]> L F FL ′]]> |L s / F FL ′|]]> |L / F FL ′|]]> 14 5.505 5.962 -1.914 2.876 3.115 15 5.195 5.205 -2.104 2.469 2.474 16 5.751 6.500 -1.956 2.940 3.323 17 5.559 6.155 -1.838 3.024 3.349 18 5.796 6.501 -1.884 3.076 3.451

[0168] Table 2:

[0169] Figure [D2]

[00038] D i ]]> D2 / D i ]]> 14 2.327 3.840 0.606 15 2.267 3.840 0.590 16 2.374 3.840 0.618 17 2.343 3.840 0.610 18 2.444 3.840 0.637

[0170] Table 3:

[0171] Figure [RH1] [RH2] F FLH ′]]> 14 -1.361 -101.469 -2.805 15 -1.596 -20.052 -3.526 16 -1.383 -55.220 -2.884 17 -1.356 -12,076 -3.106 18 -1.444 13.622 -2.654

[0172] Table 4:

[0173] Figure [N2*RVL2]

[00100] N i *RVL i ]]> [ N i * RVL i / N2 * RVL2 ] 14 0.299 0.531 1.774 15 0.324 0.535 1.646 16 0.302 0.522 1.725 17 0.307 0.532 1.731 18 0.286 0.572 2.004

[0174] Figure 19 An apparatus 50 according to the application is shown schematically. The apparatus 50 can be a microscope or a mobile device. The apparatus 50 comprises the optical assembly 1 according to the application described above. It has the features and advantages already mentioned in this regard. The optical assembly 1 can be configured as an objective 51 and / or contain an image acquisition device, for example a camera, in particular.

[0175] List of Figures:

[0176] 1 optical assembly

[0177] 2 central axis

[0178] 3 object side

[0179] 4 image side

[0180] 5 object / object plane

[0181] 6 image plane / detector

[0182] 7 first converging lens

[0183] 8 second converging lens

[0184] 9 main beam

[0185] 10 catadioptric assembly

[0186] 11 first optically partially mirror-coated optical member

[0187] 12 second optical member locally mirror coated

[0188] 13 front face

[0189] 14 back face

[0190] 14 front face

[0191] 16 back face

[0192] 17 beam path

[0193] 18 entrance pupil / stop

[0194] 19 third optical member

[0195] 21 radially inner region

[0196] 22 radially outer region

[0197] 23 mirror coating

[0198] 24 radially inner region

[0199] 25 radially outer region

[0200] 26 mirror coating

[0201] 27 diverging lens

[0202] 28 plane parallel plate

[0203] 29 front face

[0204] 30 back face

[0205] 31 first reflecting optical surface, primary mirror

[0206] 32 second reflecting optical surface, secondary mirror

[0207] 33 front face

[0208] 34 back face

[0209] 35 radially inner region

[0210] 36 radially outer region

[0211] 37 radially inner region

[0212] 38 radially outer region

[0213] 40 field lens group

[0214] 41 lens with negative refractive power, diverging lens

[0215] 42 lens with negative refractive power, diverging lens

[0216] 43 lens with negative refractive power, diverging lens

[0217] 44 lens with positive refractive power, converging lens

[0218] 50 device

[0219] 51 objective

[0220] A i ′ object

[0221] A i ′ imaging

[0222] D i Diameter of exit pupil, diameter of detector or its image diagonal

[0223] d0 Diameter of beam

[0224] d1 Diameter of entrance pupil

[0225] d2 Diameter of entrance pupil

[0226] L s Distance of object-side vertex from image plane

[0227] L0 Distance of entrance pupil from image plane or detector

[0228] h o Height of marginal ray R0

[0229] h1 Height of beam R1

[0230] R0 Marginal ray

[0231] R1 Beam

[0232] rvl o Direction cosine of marginal ray R0

[0233] rvl1 Direction cosine of beam R1

[0234] γ Principal ray angle

[0235] γ' Principal ray angle

Claims

1. An optical component (1), the optical component comprising a central axis (2), an object side (3), an image side (4), and a catadioptric component (10), The catadioptric assembly includes a first mirror coating (23) with converging refractive power and a subsequent mirror coating (26) with diverging refractive power, and the optical assembly (1) has a maximum structural space of 25 mm and a maximum linear shading of 40% along the central axis (2) from the object side (3) to the image side (4). The catadioptric component (10) includes: The optical components are arranged sequentially along the central axis (2) in the beam path (17), with a first optical component (11) partially mirror-coated on the object side (13) and a second optical component (12) partially mirror-coated on the object side (15) and a second optical component (16) on the image side (14). The first optical component (11) is arranged on the image side of the second optical component (12). The first optical component (11) includes a radially inner region (21) and a radially outer region (22) about the central axis (2), wherein the inner region (21) is configured to be at least partially transmissive for object-side incident light, and the outer region (22) on the back surface (14) is configured to be reflective for object-side incident light. Furthermore, the second optical component (12) comprises a radially inner region (24) and a radially outer region (25) about the central axis (2), wherein the outer region (25) is configured to be transmissive for light incident from the object side, while the inner region (24) is configured to be reflective for light incident from the image side. In the beam path (17), at least a first refractive surface and a second refractive surface with refractive power are arranged between the back surface (14) of the first optical component (11) and the front surface (15) of the second optical component (12). The back surface of the first optical component (11) with the partial mirror coating is continuous, and The first mirror coating (23) is on the back side of the first optical component (11), and the subsequent mirror coating (26) is on the second optical component (12).

2. The optical component (1) according to claim 1, in, The first refractive surface with refractive power is formed by the front side (13) of the first optical component (11), and / or the second refractive surface with refractive power is formed by the back side (16) of the second optical component (12).

3. The optical component (1) according to claim 1 or claim 2, in, The first optical component (11) is designed such that only the front side (13) and / or the back side (14) have refractive power, and the image plane is arranged directly on the image side of the first optical component (11).

4. The optical component (1) according to claim 1 or claim 2, in, In a geometric sense and in the beam path (17), at least one third optical element (19) is arranged between the first optical element (11) and the second optical element (12).

5. The optical component (1) according to claim 4, in, The at least one third optical element (19) is designed to be refractive, and / or The at least one third optical component (19) is designed to correct at least one imaging error.

6. The optical component (1) according to claim 1 or claim 2, in, The radial extension dimensions of the individual optical components (11, 12, 19) of the optical assembly (1) differ from each other by a maximum of 2 mm or a maximum of 30%.

7. The optical component (1) according to claim 1 or claim 2, in, At least one field lens is arranged in the beam path (17) and / or geometrically between the catadioptric assembly (10) and the image side (6).

8. The optical component (1) according to claim 7, in, In the beam path (17) and / or geometrically, at least one field lens group (40) is arranged between the catadioptric assembly (10) and the image side (4) of the optical assembly (1), the at least one field lens comprising at least one lens (44) with positive refractive power and at least one lens (41, 42, 43) with negative refractive power, or the at least one field lens comprising at least one lens (41, 42, 43) with negative refractive power.

9. The optical component (1) according to claim 8, in, The field lens group (40) includes a first lens or a lens group (44) with positive refractive power, and a second lens or a lens group (41, 42, 43) with negative refractive power, wherein the second lens or the lens group with negative refractive power is arranged in front of the first lens or the lens group (44) with positive refractive power in the beam path (17).

10. The optical component (1) according to claim 7, in, The radial inner region (21) of the first optical component (11) has negative refractive power.

11. The optical component (1) according to claim 1 or claim 2, in, A field lens group (40) is arranged on the image side of the catadioptric assembly (10), and the optical assembly (1) defines an image plane (6), wherein The optical component (1) has a structural length L measured from the vertex of the first optical surface to the image plane (6). s And the field lens group (40) has a paraxial focal length f' FL The focal length is less than zero (f') FL <0), and wherein the paraxial focal length f' FL The absolute value is less than the structural length L s (|f' FL | <L s ), and wherein the first optical surface is the front side of the catadioptric component or the second optical component.

12. The optical component (1) according to claim 1 or claim 2, in, At least one field lens (41-44) is arranged on the image side of the catadioptric assembly (10), and the optical assembly (1) defines an image plane (6) having an imaging plane with a diameter of D1, wherein the optical assembly (1) has a free optical diameter D2 on the image side of the back side (34) of the catadioptric assembly (10) or the back side (14) of the first optical member (11), wherein the ratio of the free optical diameter D2 to the diameter D1 of the imaging plane is less than 1 (D2 / D1<1).

13. The optical component (1) according to claim 1 or claim 2, in, At least one field lens (41-44) is arranged on the image side of the catadioptric assembly (10), and the optical assembly (1) defines an image plane (6), wherein the optical assembly (1) has a focal length f' and a structural length L measured from the vertex of the first optical surface to the image plane (6). s The focal length f' is related to the structural length L s The ratio is greater than 2 (f' / L) s >2), and wherein the first optical surface is the front side of the catadioptric component or the second optical component.

14. The optical component (1) according to claim 1 or claim 2, in, At least one field lens (41-44) is arranged on the image side of the catadioptric assembly (10), and the optical assembly (1) defines an image plane (6), wherein the optical assembly (1) has an imaging scale β, a distance FWD from the object plane to the vertex of the first optical surface, and a structural length L measured from the vertex of the first optical surface to the image plane (6). s And the distance FWD and the structural length L s The product of the quotient and the imaging ratio β is greater than 2 (FWD / L) s *β>2), and wherein the first optical surface is the front side of the catadioptric component or the second optical component.

15. The optical component (1) according to claim 1 or claim 2, in, The principal beam angle of the beam path (17) has a direction cosine rvl2 on the back surface (34) of the catadioptric assembly (10) or the back surface (14) of the first optical component (11) before leaving the catadioptric assembly (10), the catadioptric assembly (10) has a refractive index n2 on the back surface, and the principal beam angle of the beam path (17) has a direction cosine rvl1 in the image-side medium with a refractive index n1 in the image plane (6), where (n2*rvl2) / (n1*rvl1)<1.

16. The optical component (1) according to claim 1 or claim 2, in, The optical component (1) has a negative imaging ratio and / or a positive entrance pupil position and / or a positive exit pupil position.

17. The optical component (1) according to claim 1 or claim 2, in, The number of reflections along the beam path (17) is even.

18. The optical component (1) according to claim 1 or claim 2, in, The optical component (1) has an aperture stop, and the distance between the object plane (5) defined by the optical component (1) and the aperture stop is greater than the distance between the aperture stop and the image plane (6) defined by the optical component (1).

19. The optical component (1) according to claim 1 or claim 2, in, At least one of the optical surfaces is configured to be continuous and at least once differentiable in the beam path (17).

20. The optical component (1) according to claim 1 or claim 2, in, The optical component (1) is designed as a microscope and / or as a mobile device.

21. An objective lens (51) comprising an optical component (1) according to any one of the preceding claims.

22. An image acquisition device or an image reproduction device, the image acquisition device or image reproduction device comprising the objective lens (51) according to claim 21.

23. An apparatus (50) comprising an image acquisition device or an image reproduction device according to claim 22 or an optical component (1) according to any one of claims 1 to 20.

Images