Optical system

Abstract

Disclosed in the present invention is an optical system, sequentially comprising, from the rear side to the front side, an aperture located on the rear side of the optical system, a first lens, a second lens, a circular polarizer, and an image plane. The circular polarizer is attached to the rear side surface of the image plane; a composite film is arranged provided on the rear side surface of the first lens; the composite film comprises a reflective polarizing film and a quarter-wave plate; and the reflective polarizing film is provided on the rear side of the quarter-wave plate. The maximum semi-diameter of the first lens and the second lens is Max SD, the focal length of the optical system is f, the focal length of the first lens is f1, the focal length of the second lens is f2, the central radius of curvature of the front side surface of the second lens is R4, and the following relational expressions are satisfied: Max SD ≤ 25.60 mm; -0.61 ≤ R4 / f2 ≤ -0.17; and 19.00 ≤ |f1 / f| + |f2 / f| ≤23.20.

Description

Optical system Technical Field

[0001] This invention relates to the field of near-eye display technology, and in particular to an optical system. Background Technology

[0002] With the rapid development of smart head-mounted device technology in recent years, electronic devices equipped with optical lenses have become more widely used, and the requirements for optical lenses have become more diversified. Applications in virtual reality, augmented reality, and mixed reality are growing rapidly. From the perspective of user experience, there is an urgent need for optical systems that combine small size and excellent imaging methods.

[0003] Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide an optical system that, while possessing excellent optical performance, meets the design requirements of miniaturization and lightweight design.

[0005] To solve the above-mentioned technical problems, embodiments of the present invention provide an optical system, which includes, from rear to front, an aperture located at the rear of the optical system.

[0006] First lens;

[0007] Second lens;

[0008] Circular deflector;

[0009] Image surface;

[0010] The circular polarizer is attached to the rear side of the image plane; a composite film is provided on the rear side of the first lens; the composite film includes a reflective polarizing film and a quarter-wave plate, and the reflective polarizing film is disposed on the rear side of the quarter-wave plate.

[0011] The maximum half-aperture of the first lens and the second lens is Max SD, the focal length of the optical system is f, the focal length of the first lens is f1, the focal length of the second lens is f2, and the central radius of curvature of the front side of the second lens is R4, and the following relationships are satisfied: Max SD≤25.60mm; -0.61≤R4 / f2≤-0.17; 19.00≤|f1 / f|+|f2 / f|≤23.20.

[0012] Preferably, the on-axis thickness of the first lens is d2 and the on-axis thickness of the second lens is d4, satisfying the following relationship: 0.20≤d2 / d4≤1.40.

[0013] Preferably, the eyebox size of the optical system satisfies the following relationship: eyebox ≥ 12.00 mm.

[0014] Preferably, the on-axis distance from the human eye to the rear side of the first lens is eyerelief, which satisfies the following relationship: eyerelief≤15.00mm.

[0015] Preferably, the axial distance from the rear side of the first lens to the image plane is TL, which satisfies the following relationship: TL≤19.10mm.

[0016] Preferably, the total optical length of the optical system is TTL, satisfying the following relationship: TTL≤31.10mm.

[0017] Preferably, the rear and front surfaces of the first lens and the rear and front surfaces of the second lens are both aspherical.

[0018] Preferably, the field of view (FOV) of the 1.0 field of view of the optical system is 95.00°≤FOV≤105.00°.

[0019] Preferably, the front surface of the second lens is coated with a semi-transparent and semi-reflective film.

[0020] Preferably, the transmissivity and reflectivity of the semi-transparent and semi-reflective film are both 40.00%-60.00%.

[0021] Preferably, the transmittance of the reflective polarizing film is greater than or equal to 95.00%.

[0022] Preferably, the optical distortion of the optical system is MIST, which satisfies the following relationship: MIST ≤ 35.00%.

[0023] Preferably, the chromatic difference of the optical system is LC, which satisfies the following relationship: LC≤25μm.

[0024] Preferably, the total optical length of the optical system is TTL, satisfying the following relationship: TTL / f≤1.38.

[0025] The beneficial effects of this invention are as follows: a composite film consisting of a reflective polarizing film and a quarter-wave plate is disposed on the rear side of the first lens, and a semi-transparent, semi-reflective film is disposed on the front side of the second lens. This achieves an optical path folding structure through the participation of two lenses, significantly reducing the total optical length (TTL) of the optical system, thereby reducing the size of the optical imaging module. This meets the design requirements of miniaturization and lightweighting for VR devices, combining small size with high imaging performance. Furthermore, the optical system provided by this invention allows users to achieve optimal display effects without cumbersome adjustments, effectively improving the user experience. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0027] Figure 1 is a schematic diagram of the optical system according to the first embodiment of the present invention;

[0028] Figure 2 is a point array diagram of the optical system shown in Figure 1;

[0029] Figure 3 is a schematic diagram of the magnification chromatic aberration of the optical system shown in Figure 1;

[0030] Figure 4 is a schematic diagram of the field curvature and distortion of the optical system shown in Figure 1;

[0031] Figure 5 is a schematic diagram of the optical system shown in Figure 1, including the film structure.

[0032] Figure 6 is a partial structural schematic diagram of the optical system according to the second embodiment of the present invention;

[0033] Figure 7 is a point array schematic diagram of the optical system shown in Figure 6;

[0034] Figure 8 is a schematic diagram of the magnification chromatic aberration of the optical system shown in Figure 6;

[0035] Figure 9 is a schematic diagram of the field curvature and distortion of the optical system shown in Figure 6;

[0036] Figure 10 is a schematic diagram of the optical system shown in Figure 6, including the film structure.

[0037] Figure 11 is a partial structural schematic diagram of the optical system according to the third embodiment of the present invention;

[0038] Figure 12 is a point array diagram of the optical system shown in Figure 11;

[0039] Figure 13 is a schematic diagram of the magnification chromatic aberration of the optical system shown in Figure 11;

[0040] Figure 14 is a schematic diagram of the field curvature and distortion of the optical system shown in Figure 11;

[0041] Figure 15 is a schematic diagram of the optical system shown in Figure 11, including the film structure. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the various embodiments of this invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this invention to facilitate a better understanding of the invention. However, the technical solutions claimed in this invention can be implemented even without these technical details and with various variations and modifications based on the following embodiments.

[0043] Referring to Figures 1-15, the technical solution of the present invention provides an optical system 100, 200, and 300. Figures 1, 6, and 11 show the optical system 100, 200, and 300 of the present invention, which includes two lenses. Specifically, the optical system 100, 200, and 300, from rear to front, sequentially includes: an aperture 11, a reflective polarizing film 12, a quarter-wave plate 13, a first lens 14, a first anti-reflection film 15, a second anti-reflection film 16, a second lens 17, a semi-transparent and semi-reflective film 18, a circular polarizer 19, and an image surface 20. In the present invention, the image surface 20 is a display screen; it should be noted that, in the present invention, the rear side is the side where the human eye is located, i.e., the position of the aperture 11, and the front side is the side where the display screen is located. The front side refers to the surface facing the display screen side in the optical axis direction, and the rear side refers to the surface facing the human eye side in the optical axis direction.

[0044] Specifically, the light emitted from the image surface 20 is circularly polarized after passing through the circular polarizer 19. This circularly polarized light is incident on the semi-transparent and semi-reflective coating 18 on the front side 172 of the second lens 17. Part of the light is reflected, and part of the light is incident on the second lens 17. At this time, the light incident on the second lens 17 is still circularly polarized. This circularly polarized light passes sequentially through the second anti-reflection coating 16, the first anti-reflection coating 15, and the first lens 14.

[0045] Because the rear surface 141 of the first lens 14 is provided with a composite film consisting of a reflective polarizing film 12 and a quarter-wave plate 13, and the quarter-wave plate 13 is closer to the rear surface 141 of the first lens 14 than the reflective polarizing film 12, the circularly polarized light emitted from the first lens 14 is converted into linearly polarized S-light after passing through the quarter-wave plate 13 for the first time. Subsequently, the linearly polarized S-light is reflected at the reflective polarizing film 12, and the reflected light is still linearly polarized S-light. The linearly polarized S-light is converted into circularly polarized light after passing through the quarter-wave plate 13 for the second time. After the circularly polarized light is incident on the first lens 14 for the second time, it passes through the first anti-reflection film 15, the second anti-reflection film 16, the third anti-reflection film 17, the fourth anti-reflection film 18, the fifth anti-reflection film 19, the sixth anti-reflection film 19, the seventh anti-reflection film 19, the eighth anti-reflection film 19, the ninth anti-reflection film 19, the eleventh ... After passing through the second antireflection coating 16 and the second lens 17, partial reflection occurs at the semi-reflective coating 18. The reflected circularly polarized light has the opposite polarization direction to the incident circularly polarized light. This reflected circularly polarized light then enters the second lens 17 for the third time. After exiting the second lens 17, it passes sequentially through the second antireflection coating 16, the first antireflection coating 15, and the first lens 14 before entering the quarter-wave plate 13. After passing through the quarter-wave plate 13, it is transformed into linearly polarized P-light and enters the reflective polarization coating 12. Because the reflective polarization coating 12 has the characteristic of reflecting linearly polarized S-light and transmitting linearly polarized P-light, the linearly polarized P-light is transmitted through the reflective polarization coating 12 and enters the aperture 11. The aperture 11 is positioned to simulate the surface of the human eye.

[0046] A composite film consisting of a reflective polarizing film 12 and a quarter-wave plate 13 is provided on the rear side 141 of the first lens 14. By utilizing the optical path folding structure, the volume of the optical system is reduced. A semi-transparent and semi-reflective film 18 is provided on the front side 172 of the second lens 17. By employing the first lens 14 and the second lens 17 to participate in the folding optical path scheme, the total optical length of the optical system is greatly reduced, which is conducive to the miniaturization and lightweight development trend of VR devices.

[0047] The maximum half-aperture of the first lens 14 and the second lens 17 is defined as Max SD, which satisfies the following relationship: Max SD ≤ 25.60 mm. Within the range of the condition, it is beneficial to reduce the size of the optical system.

[0048] The central radius of curvature of the front side surface 172 of the second lens 17 is defined as R4, and the focal length of the second lens 17 is f2, satisfying the following relationship: -0.61≤R4 / f2≤-0.17. By reasonably setting the radius of curvature of the lens surface near the screen, the divergence angle of the light emitted by the display can be better matched, improving energy utilization and enhancing the uniformity of the display brightness of the optical system.

[0049] The focal length of the optical system is defined as f, the focal length of the first lens 14 is f1, and the focal length of the second lens 17 is f2, satisfying the following relationship: 19.00≤|f1 / f|+|f2 / f|≤23.20. Within the range of the condition, by reasonably designing the focal lengths of the first and second lenses, the field of view of the optical system can be increased, the sensitivity can be effectively reduced, the imaging effect can be improved, and the thickness of the lens group can be reduced to meet the requirements of VR devices to be thinner and lighter.

[0050] The on-axis thickness of the first lens 14 is defined as d2, and the on-axis thickness of the second lens 17 is defined as d4, satisfying the following relationship: 0.20≤d2 / d4≤1.40. Within the range of the condition, the center thickness of each lens is reasonably allocated, which is beneficial to reduce the sensitivity of the optical system, improve the production yield, and at the same time make the structure of the optical system compact, realizing the ultra-thinness of the optical system.

[0051] The eyebox size of the optical system is defined as ≥12.00mm. Within a certain range, this allows users to see the best display effect from the optimal position without cumbersome adjustments, increasing the field of view (FOV) to 90°. For easier understanding, the eyebox size can be considered the sum of the entrance pupil diameter (ENPD) of the optical system (4mm) and the eye-shift range (eyeshift ±4mm). By setting the eyebox ≥12.00mm, the full field of view performance of the optical system is improved, enhancing the user's display experience when their glasses are not properly positioned.

[0052] The on-axis distance from the human eye to the rear side 141 of the first lens 14 is defined as eyerelief, which is the on-axis distance from the aperture 11 to the rear side 141 of the first lens 14. This is the space where other structures (such as mechanical mechanisms, eyeglasses, etc.) can be placed. If eyerelief ≤ 15.00 mm, within the conditional range, while satisfying the eye's comfort, the total optical length of the optical system can be made smaller, which is beneficial for miniaturization.

[0053] The axial distance from the rear side surface 141 of the first lens 14 to the image plane 20 is defined as TL, which satisfies TL≤19.10mm. Within the conditional range, this is beneficial for the miniaturization of the optical system.

[0054] The total optical length of the optical system is defined as TTL, which is the on-axis distance from the human eye to the image plane 20, i.e. the on-axis distance from the aperture 11 to the image plane 20. It satisfies TTL≤31.10mm, which is within the conditional range and is conducive to the miniaturization of the optical system.

[0055] The rear surface 141 and front surface 142 of the first lens 14, and the rear surface 171 and front surface 172 of the second lens 17 are both aspherical. By adjusting the focus position of the displayed image through aspherical design, chromatic aberration and distortion of the displayed image are reduced, thereby improving image quality.

[0056] The field of view (FOV) of the optical system is defined as 1.0 field of view, satisfying the following relationship: 95.00°≤FOV≤105.00°. Within this condition, the user's immersion when using the device is improved, providing a more realistic VR environment.

[0057] In this invention, the transmittance and reflectance of the semi-transparent and semi-reflective film 18 on the front side 172 of the second lens 17 are both 40.00%-60.00%; for example, in various embodiments, it can be 50:50, 40:60, 60:40, etc.

[0058] In this invention, the transmittance of the reflective polarizing film 12 is greater than or equal to 95%. Higher transmittance improves the light efficiency of the optical system and increases display brightness.

[0059] The optical distortion of an optical system is defined as MIST, which satisfies MIST≤35.00%. Within the conditional range, the distortion of the optical system is small, providing users with a more realistic VR environment.

[0060] The chromatic difference of the optical system is defined as LC, which satisfies LC≤25μm. Within the conditional range, the chromatic difference of the optical system is small, providing users with a more realistic VR environment.

[0061] Define the focal length of the optical system as f, satisfying TTL / f≤1.38. Within the range of the condition, this is beneficial for reducing the size of the optical system.

[0062] (First Implementation)

[0063] The optical system 100 of the present invention will be described below with examples. The symbols used in each example are shown below. The units for focal length, on-axis distance, central radius of curvature, and on-axis thickness are mm.

[0064] Figures 1 and 5 show the optical system 100 of the first embodiment of the present invention.

[0065] Tables 1 and 2 show the design data of the optical system 100 according to the first embodiment of the present invention.

[0066] Table 1

[0067] The meanings of each symbol are as follows.

[0068] R: Radius of curvature at the center of the optical surface;

[0069] R1: The central radius of curvature of the rear surface 141 of the first lens 14;

[0070] R2: The central radius of curvature of the front surface 142 of the first lens 14;

[0071] R3: The central radius of curvature of the rear side surface 171 of the second lens 17;

[0072] R4: The central radius of curvature of the front surface 172 of the second lens 17;

[0073] d: The on-axis thickness of the lens and the on-axis distance between lenses (to facilitate understanding of the light path, the propagation of light from the front to the back is set to a positive value, and the propagation of light from the back to the front is set to a negative value; for example, in Table 1, d4 represents the light propagating from the front side 172 of the second lens 17 to the back side 171 of the second lens 17, which is a positive value; d5 represents the light propagating from the back side 171 of the second lens 17 to the front side 172 of the second lens 17, which is a negative value).

[0074] d0: The on-axis distance from aperture 11 to the rear surface 141 of the first lens 14;

[0075] d1: On-axis thickness of the reflective polarizing film 12 and the quarter-wave plate 13;

[0076] d2: On-axis thickness of the first lens 14;

[0077] d3: The on-axis distance from the front surface 142 of the first lens 14 to the rear surface 171 of the second lens 17;

[0078] d4: On-axis thickness of the second lens 17;

[0079] d5: The negative value of the on-axis thickness of the second lens 17;

[0080] d6: The negative value of the on-axis distance from the front surface 142 of the first lens 14 to the rear surface 171 of the second lens 17;

[0081] d7: The negative value of the on-axis thickness of the first lens 14;

[0082] d8: The negative value of the on-axis thickness of the quarter-wave plate 13;

[0083] d9: On-axis thickness of quarter-wave plate 13;

[0084] d10: The axial distance from the front surface 172 of the second lens 17 to the rear surface 191 of the circular polarizer 19;

[0085] d11: On-shaft thickness of the circular deflector 19;

[0086] nd: Refractive index of the d-line (the d-line represents green light with a wavelength of 550 nm);

[0087] nd1: The refractive index of the d-line of the first lens 14;

[0088] nd2: The refractive index of the d-line of the second lens 17;

[0089] ng: The refractive index of the d-line of the circular polarizer 19;

[0090] vd: Abbe number;

[0091] v1: Abbe number of the first lens 14;

[0092] v2: Abbe number of the second lens 17;

[0093] vg: Abbe number of the circular deflector 19.

[0094] Table 2 shows the aspherical data of each lens in the optical system 100 of the first embodiment of the present invention.

[0095] Table 2

[0096] For convenience, the aspherical surfaces of each lens surface are those shown in formula (1) below. However, the present invention is not limited to the aspherical polynomial form represented by formula (1). z=(cr 2 ) / {1+[1-(k+1)(c 2 r 2 )] 1 / 2}+A4r 4 +A6r 6 +A8r 8 +A10r 10 +A12r 12 +A14r 14 +A16r 16 (1)

[0097] Where k is the conic coefficient, A4, A6, A8, A10, A12, A14, and A16 are aspheric coefficients, c is the curvature at the center of the optical surface, r is the perpendicular distance between a point on the aspheric curve and the optical axis, and z is the aspheric depth (the perpendicular distance between a point on the aspheric surface at a distance r from the optical axis and the tangent plane at the vertex of the aspheric optical axis).

[0098] Figures 2 and 3 show dot plots and magnification chromatic aberration diagrams of light with wavelengths of 516 nm, 526 nm, 536 nm, 546 nm, and 556 nm after passing through the optical system 100 of the first embodiment, respectively. Figure 4 shows the field curvature and distortion diagram of light with a wavelength of 536 nm after passing through the optical system 100 of the first embodiment. In Figure 4, the field curvature S is the field curvature in the sagittal direction, and T is the field curvature in the meridional direction.

[0099] In this embodiment, the entrance pupil diameter ENPD of the optical system 100 is 12.00 mm, the image height IH of the full field of view (1.0 field of view) is 19.000 mm, and the field of view (FOV) of the full field of view (1.0 field of view) in the diagonal direction is 100.00°. The optical system 100 meets the design requirements of miniaturization and lightweight, its on-axis and off-axis chromatic aberrations are fully corrected, and it has excellent optical characteristics.

[0100] It is understandable that the 1.0 field of view image height refers to half the diagonal length of the image area, and the FOV in the diagonal direction of the 1.0 field of view refers to the field of view angle corresponding to the image area.

[0101] (Second Implementation)

[0102] The second implementation method is basically the same as the first implementation method, and the symbols have the same meanings as the first implementation method. Only the differences are listed below.

[0103] Figures 6 and 10 show the optical system 200 according to the second embodiment of the present invention. Tables 3 and 4 show the design data of the optical system 200 according to the second embodiment of the present invention.

[0104] Table 3

[0105] Table 4 shows the aspherical data of each lens in the optical system 200 of the second embodiment of the present invention.

[0106] Table 4

[0107] Figures 7 and 8 show dot plots and magnification chromatic aberration diagrams of light with wavelengths of 516 nm, 526 nm, 536 nm, 546 nm, and 556 nm after passing through the optical system 200 of the second embodiment, respectively. Figure 9 shows the field curvature and distortion diagram of light with a wavelength of 536 nm after passing through the optical system 200 of the second embodiment. In Figure 9, the field curvature S is the field curvature in the sagittal direction, and T is the field curvature in the meridional direction.

[0108] In this embodiment, the entrance pupil diameter ENPD of the optical system 100 is 12.00 mm, the image height IH of the full field of view (1.0 field of view) is 19.152 mm, and the field of view (FOV) of the full field of view (1.0 field of view) diagonal direction is 104.52°. The optical system 200 meets the design requirements of miniaturization and lightweight, its on-axis and off-axis chromatic aberrations are fully corrected, and it has excellent optical characteristics.

[0109] (Third Implementation)

[0110] The third implementation method is basically the same as the first implementation method, and the symbols have the same meanings as the first implementation method. Only the differences are listed below.

[0111] Figures 11 and 15 show the optical system 300 of the third embodiment of the present invention.

[0112] Tables 5 and 6 show the design data of the optical system 300 according to the third embodiment of the present invention.

[0113] Table 5

[0114] Table 6 shows the aspherical data of each lens in the optical system 300 of the third embodiment of the present invention.

[0115] Table 6

[0116] Figures 12 and 13 show dot plots and magnification chromatic aberration diagrams of light with wavelengths of 516 nm, 526 nm, 536 nm, 546 nm, and 556 nm after passing through the optical system 300 of the third embodiment, respectively. Figure 14 shows the field curvature and distortion diagram of light with a wavelength of 536 nm after passing through the optical system 300 of the third embodiment. In Figure 14, the field curvature S is the field curvature in the sagittal direction, and T is the field curvature in the meridional direction.

[0117] In this embodiment, the entrance pupil diameter ENPD of the optical system 300 is 12.00 mm, the image height IH of the full field of view (1.0 field of view) is 19.152 mm, and the field of view (FOV) of the full field of view (1.0 field of view) diagonal direction is 104.75°. The optical system 300 meets the design requirements of miniaturization and lightweight, its on-axis and off-axis chromatic aberrations are fully corrected, and it has excellent optical characteristics.

[0118] Table 7

[0119] Those skilled in the art will understand that the above embodiments are specific implementations of the present invention, and in practical applications, various changes can be made in form and detail without departing from the spirit and scope of the present invention.

Claims

1. An optical system characterized by comprising: From back to front, sequentially comprising: an aperture, located at the back side of the optical system; a first lens; a second lens; a circular polarizer; an image plane; wherein the circular polarizer is attached to the back side of the image plane; the back side of the first lens is provided with a composite film; the composite film comprises a reflective polarizing film and a quarter-wave plate, and the reflective polarizing film is located at the back side of the quarter-wave plate; the maximum half aperture of the first lens and the second lens is Max SD, the focal length of the optical system is f, the focal length of the first lens is f1, the focal length of the second lens is f2, the central curvature radius of the front side of the second lens is R4, and the following relationships are satisfied: Max SD≤25.60mm; -0.61≤R4 / f2≤-0.17; 19.00≤|f1 / f|+|f2 / f|≤23.

20.

2. The optical system of claim 1, wherein the on-axis thickness of the first lens is d2, and the on-axis thickness of the second lens is d4, and the following relationship is satisfied: 0.20≤d2 / d4≤1.

40.

3. The optical system of claim 1, wherein The eyebox size of the optical system is eyebox, and the following relationship is satisfied: eyebox≥12.00mm.

4. The optical system of claim 1, wherein The on-axis distance from the human eye to the back side of the first lens is eyerelief, and the following relationship is satisfied: eyerelief≤15.00mm.

5. The optical system of claim 1, wherein The on-axis distance from the back side of the first lens to the image plane is TL, and the following relationship is satisfied: TL≤19.10mm.

6. The optical system of claim 1, wherein The total optical length of the optical system is TTL, and the following relationship is satisfied: TTL≤31.10mm.

7. The optical system of claim 1, wherein The back side and the front side of the first lens and the back side and the front side of the second lens are aspheric surfaces.

8. The optical system of claim 1, wherein, The field of view angle of 1.0 field of view of the optical system is FOV, and the following relationship is satisfied: 95.00°≤FOV≤105.00°.

9. The optical system of claim 1, wherein, The front side of the second lens is coated with a semi-transparent and semi-reflective film.

10. The optical system of claim 9, wherein, The transmittance and reflectance of the semi-transparent and semi-reflective film are both 40.00%-60.00%.

11. The optical system of claim 1, wherein, The transmittance of the reflective polarizing film is greater than or equal to 95.00%.

12. The optical system of claim 1, wherein, The optical distortion of the optical system is MIST, and the following relationship is satisfied: MIST≤35.00%.

13. The optical system of claim 1, wherein, The chromatic aberration of the optical system is LC, and the following relationship is satisfied: LC≤25μm.

14. The optical system of claim 1, wherein, The total optical length of the optical system is TTL, and the following relationship is satisfied: TTL / f≤1.38.

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