Long focal length catadioptric photographic objective

Abstract

The application discloses a long-focus catadioptric photographic objective, which comprises a catadioptric lens group and a rear lens group arranged in sequence along the propagation direction of the light path; the catadioptric lens group comprises a first lens, a first reflector, a second lens, a third lens and a second reflector; the first lens is a negative meniscus lens; the second lens is a positive lens; the third lens is a negative lens; the central positions of the first lens and the first reflector are provided with light transmission holes; the rear lens group comprises a fourth lens, a fifth lens and a sixth lens arranged in sequence, and the fourth lens, the fifth lens and the sixth lens are all meniscus lenses. The long-focus catadioptric photographic objective has a long focal length of 500 mm, is small in size and light in weight, the outward extension of the rear lens group reduces the design difficulty of the mechanical structure and the debugging difficulty of assembly, and the catadioptric lens group and the rear lens group can be separated into two mechanical structures for disassembly, assembly and replacement, so that the carrying size is further reduced.

Description

Technical Field

[0001] This invention relates to a long focal length catadioptric photographic lens, belonging to the field of photographic lens technology. Background Technology

[0002] Long focal length refractive photographic lenses are generally quite long, which leads to an increased mechanical structure, resulting in problems such as large size, heavy weight, and inconvenience in carrying them. For photography enthusiasts, long focal length refractive photographic lenses cannot well meet the needs of shooting at long distances and requiring frequent camera movement. Summary of the Invention

[0003] This invention provides a long focal length catadioptric photographic objective lens, which improves upon the shortcomings of long focal length refractive photographic objectives in terms of large size and heavy weight. It provides photography enthusiasts with more choices that are more suitable for their actual situation. It is compact and lightweight, with a simple mechanical structure design, relatively simple assembly, and high practicality.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A long focal length catadioptric photographic objective includes a catadioptric lens group and a rear lens group arranged sequentially along the light path propagation direction;

[0006] Along the direction of light propagation, the catadioptric lens group includes a first lens, a first reflector, a second lens, a third lens, and a second reflector arranged sequentially; the first lens is a negative meniscus lens; the second lens is a positive lens; the third lens is a negative lens; and a light-transmitting aperture is provided at the center of both the first lens and the first reflector.

[0007] Along the direction of light propagation, the rear lens group includes a fourth lens, a fifth lens, and a sixth lens arranged in sequence, all of which are meniscus lenses;

[0008] The light propagates along the following path: after passing through the first lens, it undergoes total internal reflection by the first mirror and passes through the first lens again. It then passes through the second and third lenses in sequence, undergoes total internal reflection by the second mirror, passes through the second and third lenses again, passes through the light-transmitting aperture, and finally passes through the fourth, fifth, and sixth lenses in sequence to reach the image plane.

[0009] In the aforementioned catadioptric lens group, due to the presence of the first and second reflecting mirrors, the refracting components require light to pass through twice, allowing for the reuse of the lens and lens group, thus reducing the number of lenses used.

[0010] The second and third lenses are cemented together to form a cemented doublet lens.

[0011] Along the first propagation direction of the light path, the two sides of the first lens are, in sequence, the first lens A surface and the first lens B surface. To further reduce the size, the first reflecting mirror is a first total internal reflection film coated on the first lens B surface. The two sides of the second lens are, in sequence, the second lens A surface and the second lens B surface. The two sides of the third lens are, in sequence, the third lens A surface and the third lens B surface. The second reflecting mirror is a second total internal reflection film coated on the third lens B surface. The light path will pass through the first lens, the second lens, and the third lens twice, along the first propagation direction of the light path, that is, the direction in which the light path first passes through the first lens, the second lens, and the third lens.

[0012] To improve image quality, the radius of curvature of surface A of the first lens is -102.738±0.003mm, and the radius of curvature of surface B of the first lens (i.e., the radius of curvature of the first total reflection film) is -163.952±0.003mm; the radius of curvature of surface A of the second lens is -55.369±0.003mm, and the radius of curvature of surface B of the second lens is 398.462±0.003mm; the radius of curvature of surface A of the third lens is 398.462±0.003mm, and the radius of curvature of surface B of the third lens (i.e., the radius of curvature of the second total reflection film) is -87.256±0.003mm.

[0013] Along the direction of light propagation, the fourth lens has two surfaces that are the fourth incident surface and the fourth exit surface, the fifth lens has two surfaces that are the fifth incident surface and the fifth exit surface, and the sixth lens has two surfaces that are the sixth incident surface and the sixth exit surface. The radius of curvature of the fourth incident surface is 129.921±0.003mm, the radius of curvature of the fourth exit surface is 24.104±0.003mm, the radius of curvature of the fifth incident surface is -19.735±0.003mm, the radius of curvature of the fifth exit surface is -21.703±0.003mm, the radius of curvature of the sixth incident surface is 30.966±0.003mm, and the radius of curvature of the sixth exit surface is 44.492±0.003mm.

[0014] To achieve a better balance between image quality and size, the center thickness of the first lens (including the thickness of the first total reflection film) is 5±0.02mm, the center thickness of the second lens is 4±0.02mm, the center thickness of the third lens (including the thickness of the first total reflection film) is 4±0.02mm, the center thickness of the fourth lens is 2.2±0.02mm, the center thickness of the fifth lens is 2.2±0.02mm, and the center thickness of the sixth lens is 2.2±0.02mm.

[0015] The center-to-center distance between the first and second lenses is 57.010±0.02mm; the center-to-center distance between the second and third lenses is 0mm; the center-to-center distance between the second and fourth lenses is 64.976±0.02mm; the center-to-center distance between the fourth and fifth lenses is 6.153±0.02mm; and the center-to-center distance between the fifth and sixth lenses is 0.307±0.02mm.

[0016] To improve imaging performance, a shielding plate is provided on the backlight side of the second total internal reflection film (i.e., the shielding plate is located on the non-reflective surface, and the reflective surface is connected to the third lens). The outer diameter of the shielding plate is not less than the outer diameter of the third mirror and is less than the outer diameter of the first lens. This effectively prevents light from passing through the first total internal reflection film. The light only passes through the aperture to reach the rear lens group after being reflected by the first mirror, thus improving imaging performance.

[0017] Preferably, the outer diameter of the shielding plate is 1 to 3 mm larger than the outer diameter of the first reflecting mirror.

[0018] For ease of carrying and replacement, the catadioptric lens group and the rear lens group are set up independently, that is, the rear lens group is not inside the catadioptric lens group.

[0019] The fourth lens is a negative meniscus lens, the fifth lens is a negative meniscus lens, and the sixth lens is a positive meniscus lens.

[0020] To further improve imaging performance, the first lens has a refractive index (nd) of 1.44 and an Abbe number (vd) of 94.5; the second lens has a refractive index (nd) of 1.61 and an Abbe number (vd) of 44.1; the third lens has a refractive index (nd) of 1.69 and an Abbe number (vd) of 54.5, with a significant difference in Abbe number compared to the second lens to correct chromatic aberration. The fourth lens has a refractive index (nd) of 1.7 and an Abbe number (vd) of 48.1; the fifth lens has a refractive index (nd) of 15.9 and an Abbe number (vd) of 61.3; and the sixth lens has a refractive index (nd) of 1.53 and an Abbe number (vd) of 60.5. Their main functions are to increase image height so that the image can be received by the camera and to optimize aberrations to improve image quality.

[0021] The aforementioned telephoto catadioptric photographic objective has a system focal length of 500mm, a back focal length of 42mm, a total system length of 130mm, a total optical component length of 88mm, and an F-number of 8.

[0022] By setting the first and second reflecting mirrors in the catadioptric lens group, the lenses in the catadioptric lens group all require light to pass through twice, which can reuse the lenses and lens group, reduce the number of lenses used, and to a certain extent achieve a completely symmetrical refraction system. The rear lens group corrects aberrations and changes the exit image height of the catadioptric lens group, so that the image height reaches the size that the camera can resolve.

[0023] Any techniques not mentioned in this invention are based on existing technologies.

[0024] This invention relates to a long-focal-length catadioptric photographic objective lens with a focal length of 500mm. Compared to a simple refractive photographic objective lens, it has a shorter overall length, smaller volume, and lighter weight. The external placement of the rear lens group reduces the design difficulty of the mechanical structure and the difficulty of assembly and debugging. Furthermore, the catadioptric lens group and the rear lens group can be separated into two mechanical structures for disassembly, assembly, and replacement, further reducing the carrying volume. In addition, a total reflection coating is coated behind the first lens. After passing through the doublet lens group coated with the total reflection coating, the light that comes out passes through three rear lenses outside the catadioptric lens group to change the image height and improve the image quality before entering the camera target surface for imaging. Attached Figure Description

[0025] Figure 1 This is a layout diagram of the long focal length catadioptric photographic objective lens of the present invention.

[0026] Figure 2 This is an MTF image of the long focal length catadioptric imaging objective lens of the present invention.

[0027] Figure 3 This is the defocused MTF image of the long focal length catadioptric imaging objective lens of this invention.

[0028] Figure 4 This is a diagram showing the optical path difference of the long focal length catadioptric photographic objective lens of this invention.

[0029] Figure 5 This is an axial aberration diagram of the long focal length catadioptric imaging objective lens of this invention.

[0030] Figure 6 This is a chromatic aberration diagram of the transverse axis of the long focal length catadioptric imaging objective lens of this invention.

[0031] Figure 7 This is a light aberration diagram of the long focal length catadioptric imaging objective lens of the present invention.

[0032] Figure 8 This is a relative illumination diagram of the long focal length catadioptric photographic objective lens of the present invention.

[0033] Figure 9 This is a field curvature distortion diagram of the telephoto lens in this invention.

[0034] In the diagram, 1 is the first lens, 2 is the first reflecting mirror, 3 is the second lens, 4 is the third lens, 5 is the second reflecting mirror, 6 is the fourth lens, 7 is the fifth lens, and 8 is the sixth lens. Detailed Implementation

[0035] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0036] like Figure 1 As shown, a long focal length catadioptric photographic objective includes a catadioptric lens group and a rear lens group arranged sequentially along the light path propagation direction;

[0037] Along the direction of light propagation, the catadioptric lens group includes a first lens, a first reflector, a second lens, a third lens, and a second reflector arranged sequentially; the first lens is a negative meniscus lens; the second lens is a positive lens; the third lens is a negative lens; the second lens and the third lens are cemented together to form a cemented doublet lens; and a light-transmitting hole is provided at the center of both the first lens and the first reflector.

[0038] Along the direction of light propagation, the rear lens group includes a fourth lens, a fifth lens, and a sixth lens arranged in sequence. The fourth lens, the fifth lens, and the sixth lens are all meniscus lenses. The fourth lens is a negative meniscus lens, the fifth lens is a negative meniscus lens, and the sixth lens is a positive meniscus lens.

[0039] The light propagates along the following path: after passing through the first lens, it undergoes total internal reflection by the first mirror and passes through the first lens again. It then passes through the second and third lenses in sequence, undergoes total internal reflection by the second mirror, passes through the second and third lenses again, passes through the light-transmitting aperture, and finally passes through the fourth, fifth, and sixth lenses in sequence to reach the image plane.

[0040] Along the first propagation direction of the light path, the two sides of the first lens are, in order, the first lens A surface and the first lens B surface, and the first reflecting mirror is the first total reflection film coated on the first lens B surface; the two sides of the second lens are, in order, the second lens A surface and the second lens B surface; the two sides of the third lens are, in order, the third lens A surface and the third lens B surface, and the second reflecting mirror is the second total reflection film coated on the third lens B surface.

[0041] The aperture stop is located on surface A of the first lens;

[0042] The radius of curvature of surface A of the first lens is -102.738 mm, and the radius of curvature of surface B of the first lens and the radius of curvature of the first total internal reflection film are both -163.952 mm; the radius of curvature of surface A of the second lens is -55.369 mm, and the radius of curvature of surface B of the second lens is 398.462 mm; the radius of curvature of surface A of the third lens is 398.462 mm, and the radius of curvature of surface B of the third lens and the radius of curvature of the second total internal reflection film are both -87.256 mm; along the direction of light propagation, the two surfaces of the fourth lens are successively... The fourth incident surface and the fourth exit surface; the two sides of the fifth lens are the fifth incident surface and the fifth exit surface, respectively; the two sides of the sixth lens are the sixth incident surface and the sixth exit surface, respectively; the radius of curvature of the fourth incident surface is 129.921 mm, the radius of curvature of the fourth exit surface is 24.104 mm; the radius of curvature of the fifth incident surface is -19.735 mm, the radius of curvature of the fifth exit surface is -21.703 mm; the radius of curvature of the sixth incident surface is 30.966 mm, and the radius of curvature of the sixth exit surface is 44.492 mm.

[0043] The first lens is a negative meniscus lens with a center thickness of 5mm; the second lens is a positive lens with a center thickness of 4mm; the third lens is a negative lens with a center thickness of 4mm; the fourth lens is a negative meniscus lens with a center thickness of 2.2mm; the fifth lens is a negative meniscus lens with a center thickness of 2.2mm; and the sixth lens is a positive meniscus lens with a center thickness of 2.2mm. The center-to-center distance between the first and second lenses is 57.010mm; the center-to-center distance between the second and third lenses is 0mm; the center-to-center distance between the second and fourth lenses is 64.976mm; the center-to-center distance between the fourth and fifth lenses is 6.153mm; and the center-to-center distance between the fifth and sixth lenses is 0.307mm.

[0044] A shielding plate is provided on the back side of the aforementioned second total reflection film. The catadioptric lens group and the rear lens group are set independently.

[0045] The aforementioned telephoto catadioptric photographic objective has a system focal length of 500mm, a back focal length of 42mm, a total axis length of 130mm, a total optical length of 88mm, and an F-number of 8.

[0046] Table 1 Optical System Parameters (The table is arranged from top to bottom, which also indicates the direction of light propagation)

[0047]

[0048] The center thickness of 67mm corresponding to the above-mentioned shielding plate refers to the center distance between the shielding plate and the first lens. The shielding plate is a thin sheet that can block light, and its thickness can be within 2mm.

[0049] Figure 2The above-mentioned long focal length catadioptric imaging objective lens MTF image is from... Figure 2 It can be seen that the actual imaging effect of 100 line pairs with a resolution of 0.3 or higher is acceptable. Figure 3 The above-mentioned defocused MTF image of a long focal length catadioptric photographic objective is derived from... Figure 3 It can be seen that the focal points of different wavelengths are relatively concentrated, and the focal shift is very small. Figure 4 The above optical path difference diagram for telephoto lenses is derived from... Figure 4 It can be seen that the optical path difference is relatively small, and the aberration is small. Figure 5 The above-mentioned axial aberration diagram of the long focal length catadioptric imaging objective lens is derived from... Figure 5 It can be seen that the on-axis ball difference and on-axis color difference are acceptable. Figure 6 The above-mentioned transverse chromatic aberration diagram of the long focal length catadioptric photographic objective lens is derived from... Figure 6 It can be seen that the chromatic aberration of each wavelength is within the Airy disk. Figure 7 The above-mentioned long focal length catadioptric photographic objective lens ray aberration diagram is derived from... Figure 7 It can be seen that the optimization of various aberrations is acceptable. Figure 8 The above-mentioned relative illumination diagram of the long focal length catadioptric photographic objective lens is derived from... Figure 8 It can be seen that the relative illuminance is relatively high and the light reception is acceptable. Figure 9 The above diagram shows the field curvature distortion of the telephoto lens in catadioptric photography. Figure 9 It can be seen that the sagittal field curvature and meridional field curvature are both very small, and the distortion is within the range of 3% that can be resolved by the human eye.

Claims

1. A long focal length catadioptric photographic objective lens, characterized in that: It consists of a catadioptric lens group and a rear lens group arranged sequentially along the direction of light propagation; Along the direction of light propagation, the catadioptric lens group consists of a first lens, a first reflecting mirror, a second lens, a third lens, and a second reflecting mirror arranged sequentially; the first lens is a negative meniscus lens; the second lens is a positive lens; the third lens is a negative lens; and a light-transmitting aperture is provided at the center of the first lens and the first reflecting mirror. Along the direction of light propagation, the rear lens group consists of a fourth lens, a fifth lens, and a sixth lens arranged in sequence, all of which are meniscus lenses. The light propagates along the following path: after passing through the first lens, it undergoes total internal reflection by the first mirror and passes through the first lens again. It then passes through the second and third lenses in sequence, undergoes total internal reflection by the second mirror, passes through the second and third lenses again, passes through the light-transmitting aperture, and finally passes through the fourth, fifth, and sixth lenses in sequence to reach the image plane. Along the first propagation direction of the light path, the two surfaces of the first lens are, in sequence, the first lens A surface and the first lens B surface; the two surfaces of the second lens are, in sequence, the second lens A surface and the second lens B surface; the two surfaces of the third lens are, in sequence, the third lens A surface and the third lens B surface. The radius of curvature of surface A of the first lens is -102.738±0.003mm, and the radius of curvature of surface B of the first lens is -163.952±0.003mm; the radius of curvature of surface A of the second lens is -55.369±0.003mm, and the radius of curvature of surface B of the second lens is 398.462±0.003mm; the radius of curvature of surface A of the third lens is 398.462±0.003mm, and the radius of curvature of surface B of the third lens is -87.256±0.003mm. Along the direction of light propagation, the fourth lens has two surfaces that are the fourth incident surface and the fourth exit surface, the fifth lens has two surfaces that are the fifth incident surface and the fifth exit surface, and the sixth lens has two surfaces that are the sixth incident surface and the sixth exit surface. The radius of curvature of the fourth incident surface is 129.921±0.003mm, the radius of curvature of the fourth exit surface is 24.104±0.003mm, the radius of curvature of the fifth incident surface is -19.735±0.003mm, the radius of curvature of the fifth exit surface is -21.703±0.003mm, the radius of curvature of the sixth incident surface is 30.966±0.003mm, and the radius of curvature of the sixth exit surface is 44.492±0.003mm.

2. The long focal length catadioptric photographic objective lens as described in claim 1, characterized in that: The second and third lenses are cemented together to form a cemented doublet lens.

3. The long focal length catadioptric photographic objective lens as described in claim 1 or 2, characterized in that: The first reflecting mirror is a first total reflection film coated on the B surface of the first lens; the second reflecting mirror is a second total reflection film coated on the B surface of the third lens.

4. The long focal length catadioptric photographic objective lens as described in claim 3, characterized in that: The radius of curvature of the first total reflection film is -163.952±0.003mm; the radius of curvature of the second total reflection film is -87.256±0.003mm.

5. The long focal length catadioptric photographic objective lens as described in claim 1 or 2, characterized in that: The center thickness of the first lens is 5±0.02mm, the center thickness of the second lens is 4±0.02mm, the center thickness of the third lens is 4±0.02mm, the center thickness of the fourth lens is 2.2±0.02mm, the center thickness of the fifth lens is 2.2±0.02mm, and the center thickness of the sixth lens is 2.2±0.02mm. The center-to-center distance between the first and second lenses is 57.010±0.02mm; the center-to-center distance between the second and third lenses is 0mm; the center-to-center distance between the second and fourth lenses is 64.976±0.02mm; the center-to-center distance between the fourth and fifth lenses is 6.153±0.02mm; and the center-to-center distance between the fifth and sixth lenses is 0.307±0.02mm.

6. The long focal length catadioptric photographic objective lens as described in claim 1 or 2, characterized in that: The backlight side of the second total reflection film is provided with a shielding plate, the outer diameter of which is not less than the outer diameter of the third reflecting mirror and less than the outer diameter of the first lens.

7. The long focal length catadioptric photographic objective lens as described in claim 1 or 2, characterized in that: The catadioptric lens group and the rear lens group are set up independently.

8. The long focal length catadioptric photographic objective lens as described in claim 1 or 2, characterized in that: The first lens has a refractive index nd of 1.44 and an Abbe number vd of 94.5; the second lens has a refractive index nd of 1.61 and an Abbe number vd of 44.1; and the third lens has a refractive index nd of 1.69 and an Abbe number vd of 54.

5.

9. The long focal length catadioptric photographic objective lens as described in claim 1 or 2, characterized in that: The fourth lens has a refractive index nd of 1.7 and an Abbe number vd of 48.1; the fifth lens has a refractive index nd of 15.9 and an Abbe number vd of 61.3; and the sixth lens has a refractive index nd of 1.53 and an Abbe number vd of 60.

5.

10. The long focal length catadioptric photographic objective lens as described in claim 1 or 2, characterized in that: The system has a focal length of 500mm, a back focal length of 42mm, a total system length of 130mm, a total optical component length of 88mm, and an F-number of 8.

Images