High dynamic range infrared asteroid detection optical system based on digital micromirror device

Abstract

The invention relates to a high-dynamic-range infrared asteroid detection optical system based on a digital micromirror device. The system comprises an objective lens group, the digital micromirror device, a transpose lens group, an exit pupil and an image surface which are sequentially arranged in a light path direction, the objective lens group comprises a primary reflector, a secondary reflector and a correction lens group; the primary reflector and the secondary reflector are of an off-axis two-reflector structure; the correction lens group is used for expanding the field of view and balancing aberration; the digital micro-mirror device is used for realizing high dynamic range detection of an asteroid; the transposed lens group is used for eliminating residual aberration of an objective lens and aberration introduced by a digital micromirror device while secondary imaging; the exit pupil is the exit pupil of the transposed lens group; the image plane is a final imaging position. The digital micromirror device is added to change the deflection angle of the micromirror in the selected area in the detection process, so that the light intensity of the selected area on the image surface is modulated, and high-dynamic-range detection is realized.

Description

Technical Field

[0001] The present invention relates to the field of space optical technology, and in particular to a high dynamic range infrared asteroid detection optical system based on a digital micromirror device. Background Art

[0002] With the continuous development of human aerospace technology, deep space exploration has gradually become another development frontier and new focus in the global aerospace field after near-Earth satellite exploration and manned space flight. In astronomy, asteroids with an orbital distance of at least 0.3 astronomical units from the Earth are defined as near-Earth asteroids. Among them, asteroids with a minimum orbital distance of less than 0.05AU and a diameter greater than 140m are considered potential threatening near-Earth asteroids. Near-Earth asteroid exploration is an indispensable part of deep space exploration.

[0003] The detection of asteroids is mainly achieved through optical systems. There are three main types of optical systems for asteroid detection at home and abroad: full-transmission, full-reflection, and catadioptric. Each of these three types has its own advantages and disadvantages. The American Dawn probe uses a 20mm-diameter full-transmission optical system, a focal length of 150mm, F / #=7.9, and a field of view of 5.5°. The system can achieve full-color and 7 optional spectral band imaging; the Rosetta probe launched by the European Space Agency carries a narrow-angle camera of an off-axis three-reflection system and a wide-angle camera of an off-axis two-reflection system, which are used to obtain local high-resolution images of comets and observe the overall overview image of the comet nucleus, respectively.

[0004] When an asteroid is exposed to sunlight, it will reflect sunlight and radiate energy outward as its temperature rises. The radiation band is located in the infrared region of the electromagnetic spectrum, and is more prominent in the 3-5 micron mid-infrared band. However, when the optical system is facing deep space exploration, in addition to sunlight, the biggest influence in the mid-infrared 3-5 micron detection band is the zodiacal light, also known as the zodiacal background radiation. Similar to asteroids, interstellar dust particles will cause scattering of sunlight in the visible band, thereby forming yellow light in the visible band. At the same time, the particles are affected by solar radiation, and their own temperature changes will cause thermal radiation, forming zodiacal light in the infrared band. Its distribution is uneven, and the intensity is centered on the sun and in the ecliptic plane. With the increase of azimuth and elevation angle, the scattered stray light of the ecliptic background gradually weakens. When the asteroid is in an area of ​​the detector's field of view where the zodiacal light and sunlight are strong, the brightness of the asteroid and background radiation may exceed the dynamic range of the infrared detector, and it will be impossible to distinguish between the detection target and the background radiation. Similarly, when the asteroid is farther away and its brightness is lower, it may be lower than the dynamic range of the detector, and it will not be able to be observed. Summary of the invention

[0005] The present invention aims to solve the technical problem in the prior art that the dynamic range of the detection target and background radiation exceeds the detection dynamic range of the detector during asteroid detection, and provides a high dynamic range infrared asteroid detection optical system based on a digital micromirror device.

[0006] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0007] A high dynamic range infrared asteroid detection optical system based on a digital micromirror device, comprising: an objective lens group, a digital micromirror device, a transposition lens group, an exit pupil and an image plane arranged in sequence in the direction of an optical path;

[0008] in:

[0009] The objective lens group includes: a primary reflector, a secondary reflector and a correction lens group; the primary reflector and the secondary reflector are off-axis double-reflection structures; the function of the correction lens group is to expand the field of view and balance the aberration;

[0010] The role of digital micromirror devices is to achieve high dynamic range detection of asteroids;

[0011] The function of the transposition mirror group is to eliminate the residual aberration of the objective lens and the aberration introduced by the digital micromirror device while performing secondary imaging;

[0012] The exit pupil is the exit pupil of the transposed lens group;

[0013] The image plane is the final imaging position.

[0014] In the above technical solution, the structure of the exit pupil matches the cold screen.

[0015] In the above technical solution, the surface of the main reflector is a free-form surface, and the surface height of the main reflector is defined as:

[0016]

[0017] Among them, r 2 =x 2 +y 2 is a polar coordinate variable; is the paraxial curvature, R 0 is the radius of curvature of the surface; k is the cone coefficient; N is the total number of polynomial coefficients in the series; A i are the coefficients of the i-th expanded polynomial, which is just a power series in the x and y directions.

[0018] In the above technical solution, the surface of the secondary reflector is an even-order aspheric surface, and the secondary reflector surface sag is defined as:

[0019]

[0020] Among them, r 2 =x2 +y 2 is a polar coordinate variable; is the paraxial curvature, R 0 is the radius of curvature of the surface; k is the cone coefficient; α i are the coefficients of the higher-order terms.

[0021] In the above technical solution, the correction lens group includes: objective correction lens 1, objective correction lens 2 and objective correction lens 3;

[0022] The surface of the objective correction lens is an even-order aspheric surface;

[0023] The surface shapes of objective correction lens 2 and objective correction lens 3 are standard spherical lenses;

[0024] The surface sag of the objective correction lens is defined as:

[0025]

[0026] Among them, r 2 =x 2 +y 2 is a polar coordinate variable; is the paraxial curvature, R 0 is the radius of curvature of the surface; k is the cone coefficient; α i are the coefficients of the higher-order terms.

[0027] In the above technical solution, the transposition lens group includes: transposition lens group lens 1, transposition lens group lens 2, transposition lens group lens 3, transposition lens group lens 4 and transposition lens group lens 5;

[0028] The surface shapes of the first transfer lens group, the second transfer lens group, the third transfer lens group, the fourth transfer lens group and the fifth transfer lens group are standard spherical lenses respectively.

[0029] The present invention has the following beneficial effects:

[0030] The high dynamic range infrared asteroid detection optical system based on a digital micromirror device of the present invention modulates the light intensity of the selected area on the image plane by adding a digital micromirror device (DMD) to change the micromirror deflection angle of the selected area during the detection process, thereby realizing high dynamic range detection. At the same time, the front-end imaging objective lens area adopts the form of off-axis two-mirror and correction lens group, realizing the folding of the light path while avoiding the obstruction of the secondary mirror. In addition, the off-axis reflection can make the transposed light path after the digital micromirror device stagger with each other while having a larger entrance pupil diameter, avoiding interference between the optical elements, improving the rationality of the system, and reducing the envelope volume of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] Figure 1 (a) is a schematic diagram of the extreme optical position of a digital micromirror device (DMD), and (b) is a schematic diagram of the imaging law of an inclined object surface.

[0033] Figure 2 Schematic diagram of the optical path of the high dynamic range infrared asteroid detection optical system based on digital micromirror devices of the present invention.

[0034] Figure 3 Schematic diagram of the transfer function MTF of the high dynamic range infrared asteroid detection optical system based on digital micromirror devices of the present invention.

[0035] Figure 4 This is a schematic diagram of a standard point diagram of a high dynamic range infrared asteroid detection optical system based on a digital micromirror device according to the present invention.

[0036] Figure 5 Schematic diagram of the diffraction circle input energy of the high dynamic range infrared asteroid detection optical system based on the digital micromirror device of the present invention.

[0037] The reference numerals in the figures indicate:

[0038] 1-primary reflector; 2-secondary reflector; 3-objective correction lens 1; 4-objective correction lens 2; 5-objective correction lens 3; 6-digital micromirror device; 7-transposition lens group 1; 8-transposition lens group 2; 9-transposition lens group 3; 10-transposition lens group 4; 11-transposition lens group 5; 12-exit pupil; 13-image plane. DETAILED DESCRIPTION

[0039] The inventive concept of the present invention is:

[0040] The high dynamic range infrared asteroid detection optical system based on a digital micromirror device of the present invention solves the problem of too high or too low dynamic range making it difficult to detect in real time during asteroid detection by adopting a digital micromirror device (DMD), thereby ultimately achieving a high dynamic range detection effect and improving the detection capability for asteroids.

[0041] The high dynamic range infrared asteroid detection optical system based on digital micromirror device of the present invention uses a digital micromirror device as a light intensity regulation device, which has the advantages of high light efficiency, high reliability, and precise light intensity regulation level, and has important applications in infrared scene generation technology, three-dimensional imaging, and grating exposure lighting. Figure 1As shown in (a), the digital micromirror device is composed of millions of square tiny mirrors, each of which can be addressed individually, and has an "open state" and a "closed state", corresponding to the "ON" and "OFF" states. The digital micromirror device used in the high dynamic range infrared asteroid detection optical system based on digital micromirror devices of the present invention has a tiny mirror corresponding to the "ON" state rotated by +12°, and the incident light can enter the subsequent optical system, and a tiny mirror corresponding to the "OFF" state rotated by -12°, and the incident light no longer enters the subsequent optical system, but enters the absorption device.

[0042] The high dynamic range infrared asteroid detection optical system based on a digital micromirror device of the present invention, in order to obtain an image with a high dynamic range, places a digital micromirror device as a light intensity modulation device on the image plane of an imaging objective lens, so that a scene target is imaged on the digital micromirror device through the imaging objective lens, and then the image after light intensity modulation of the digital micromirror device is re-imaged on an imaging unit, i.e., an image sensor, through a transposed lens, thereby obtaining an image of a scene target with a high dynamic range. The light intensity modulation method of the digital micromirror device is realized by a dimming algorithm, and by controlling the deflection time and "on and off" state of micromirrors at different parts, useless light will enter the light intensity absorption device, so as to achieve high dynamic range image acquisition.

[0043] The digital micromirror device rotation axis used in the high dynamic range infrared asteroid detection optical system based on digital micromirror devices of the present invention is a diagonal line, and the stable "on and off" state is located in the direction of ±12°, so the transposition lens and the light intensity absorption device will be located in the direction of ±24°, and the line connecting the two is perpendicular to the rotation axis of the digital micromirror device. Due to space limitations, the imaging objective lens part of the present invention adopts an off-axis two-reflection structure to achieve a larger entrance pupil diameter while still having space to place the digital micromirror device and the transposition lens group to prevent interference between the components, and the off-axis system has no secondary mirror obstruction to improve system performance. At the same time, a correction lens group is added to the imaging objective optical path to expand the system field of view and correct residual aberrations, and the objective lens is kept as an image-side telecentric system, so as to cooperate with the digital micromirror device and the subsequent transposition lens group.

[0044] The high dynamic range infrared asteroid detection optical system based on digital micromirror devices of the present invention has an operating band of 3 to 5 microns in the mid-infrared. The final imaging image plane needs to use a refrigerated detector. Usually, the refrigerated detector is used in conjunction with a dewar flask and a cold screen to reduce the internal stray radiation interference of the infrared system. Therefore, a real exit pupil needs to be left in the rear transposition mirror group to add a cold aperture. At the same time, since the digital micromirror device will deflect the light, a transposition mirror group is introduced to make the inclined object plane imaged on the inclined image plane, such as Figure 1 As shown in (b), the limitations of this imaging method will also introduce corresponding aberrations, which need to be corrected by multiple lenses.

[0045] The basic parameters of the high dynamic range infrared asteroid detection optical system based on digital micromirror devices of the present invention include: working band 3 to 5 microns, entrance pupil diameter 450mm, field of view 1.4°×1° (rectangular field of view, full field of view 1.4° in the X direction, full field of view 1° in the Y direction), standard spot diagram RMS radius basically meets the Airy disk radius, system optical transfer function is greater than 0.35 at 15lp / mm, diffraction circle input energy is greater than 75% within 30 microns (see Figure 3-5 ).

[0046] The present invention is described in detail below with reference to the accompanying drawings.

[0047] The high dynamic range infrared asteroid detection optical system based on a digital micromirror device of the present invention comprises: an objective lens group, a digital micromirror device 6, a transposition lens group, an exit pupil 12 and an image plane 13 arranged in sequence in the direction of the optical path. Specifically:

[0048] The objective lens group includes: a primary reflector 1, a secondary reflector 2 and a correction lens group; wherein: the primary reflector 1 and the secondary reflector 2 are off-axis two-mirror structures, there is no obstruction between the two and no interference with the transposition lens group; the correction lens group includes: an objective correction lens 1 3, an objective correction lens 2 4 and an objective correction lens 3 5; the function of the correction lens group is to expand the field of view and balance the aberration, and while expanding the field of view, correct the residual aberration and make the objective lens telecentric;

[0049] The function of the digital micromirror device 6 is to achieve high dynamic range detection of asteroids;

[0050] The transposition mirror group includes: a transposition mirror group lens 1 7, a transposition mirror group lens 2 8, a transposition mirror group lens 3 9, a transposition mirror group lens 4 10 and a transposition mirror group lens 5 11, which functions to eliminate the residual aberration of the objective lens and the aberration introduced by the digital micromirror device 6 while performing secondary imaging;

[0051] The exit pupil 12 is the exit pupil of the transposed lens group, and is matched with the cold screen in structure;

[0052] The image plane 13 is the final imaging position.

[0053] In the high dynamic range infrared asteroid detection optical system based on digital micromirror device of the present invention, the overall focal length of the imaging objective lens part is 2500mm, and the F number is 5.56. Figure 2 and 3As shown, the off-axis double-reflection structure of the main reflector 1 and the secondary reflector 2 at the front end is compact and has good practicality. Due to its advantages such as no chromatic aberration, wide band, and large size, the reflective optical system is widely used in the structural design of various large-aperture telescopes. The traditional coaxial reflection system has the problem of central obstruction, which affects the field of view and causes the MTF value of the low frequency in the incident signal to decrease, affecting the imaging quality of the system. To solve this problem, the present invention adopts the aperture off-axis method to de-axis the coaxial system, avoid central obstruction, and improve the system performance. In order to meet the requirements of image telecentricity and aberration, free-form surfaces and aspherical surfaces are respectively adopted, and the objective lens correction lens 1 3, objective lens correction lens 2 4, and objective lens correction lens 3 5 correction lens group are inserted at the same time to correct the residual aberration while expanding the field of view and make the objective lens telecentric to the object side, so as to achieve the purpose of expanding the field of view and balancing the aberration.

[0054] The high dynamic range infrared asteroid detection optical system based on a digital micromirror device of the present invention uses the digital micromirror device 6 as the image plane of the imaging objective lens to modulate the light intensity of the area where the dynamic range needs to be increased or decreased.

[0055] The transposition lens group lens 1 7, the transposition lens group lens 2 8, the transposition lens group lens 3 9, the transposition lens group lens 4 10 and the transposition lens group lens 5 11 are combined to form a transposition lens group. The two lens groups (objective lens group and transposition lens group) are coupled at the position where the digital micromirror device 6 is located. It is required that the pixel points of the digital micromirror device 6 correspond to the pixel points of the image sensor. In order to achieve the transfer function MTF ( Figure 3 ) and ensure the correct matching of the two optical systems, the image telecentric optical path is used for the design of the imaging objective optical system. The transposition lens group is an optical system with an object-image magnification ratio of approximately 1:1, and the design adopts a quasi-symmetrical optical structure.

[0056] The high dynamic range infrared asteroid detection optical system based on a digital micromirror device of the present invention adopts a free-form surface on the surface of the main reflector 1, which is the aperture stop of the system; the secondary reflector 2 adopts an even-order aspheric surface; the objective lens correction mirror 1 3 used as a correction lens also adopts an even-order aspheric surface; the objective lens correction mirror 2 4, the objective lens correction mirror 3 5, the transposed lens group lens 1 7, the transposed lens group lens 2 8, the transposed lens group lens 3 9, the transposed lens group lens 4 10 and the transposed lens group lens 5 11 are all standard spherical lenses.

[0057] Table 1 shows the surface parameters, thickness spacing and material type of each surface.

[0058] The serial numbers 1-20 in Table 1 correspond to the following arranged in sequence in the direction of the optical path: the reflecting surface of the main reflecting mirror 1, the reflecting surface of the secondary reflecting mirror 2, the front surface of the objective lens correction lens 3, the rear surface of the objective lens correction lens 3, the front surface of the objective lens correction lens 4, the rear surface of the objective lens correction lens 4, the front surface of the objective lens correction lens 3 5, the rear surface of the objective lens correction lens 3 5, the reflecting surface of the digital micromirror device 6, the front surface of the transposed lens group lens 1 7, the rear surface of the transposed lens group lens 1 7, the front surface of the transposed lens group lens 2 8, the rear surface of the transposed lens group lens 2 8, the front surface of the transposed lens group lens 3 9, the rear surface of the transposed lens group lens 3 9, the front surface of the transposed lens group lens 4 10, the rear surface of the transposed lens group lens 4 10, the front surface of the transposed lens group lens 5 11, the rear surface of the transposed lens group lens 5 11 and the image plane 13.

[0059] The Chinese meanings of the English words in Table 1 are: DMD stands for digital micromirror device, inf stands for infinity, MIRROR stands for mirror, SILICON stands for silicon, GERMANIUM stands for germanium, KRS5 stands for thallium bromide iodide, and CSBR stands for cesium bromide.

[0060] Table 1 Optical system parameters

[0061]

[0062] The front-end off-axis two-mirror structure is realized by aperture off-axis, so the off-axis amount of the main reflector 1 in the Y direction is -350;

[0063] The surface shape of the main reflector 1 is an extended polynomial, that is, an XY polynomial, and its surface sag is defined as follows:

[0064]

[0065] Among them, r 2 =x 2 +y 2 is a polar coordinate variable; is the paraxial curvature, R 0 is the radius of curvature of the surface; k is the cone coefficient; N is the total number of polynomial coefficients in the series; A i are the coefficients of the i-th expanded polynomial, which is just a power series in the x and y directions.

[0066] The main reflector 1 surface type has 10 items in total: X1Y0, X0Y1, X2Y0, X1Y1, X0Y2, X3Y0, X2Y1, X1Y2, X0Y3, X4Y0; their values ​​are shown in Table 2:

[0067] Table 2 Extended polynomial parameters

[0068]

[0069] The surfaces of the secondary reflector 2 and the objective lens correction mirror 3 are respectively made of even-order aspheric surfaces, and their surface sag heights are defined as follows:

[0070]

[0071] Among them, r 2 =x 2 +y 2 is a polar coordinate variable; is the paraxial curvature, R 0 is the radius of curvature of the surface; k is the cone coefficient; α i are the coefficients of the higher-order terms.

[0072] Since the second-order term in the even-order aspheric surface profile sag parameter will couple with the quadratic surface coefficient k value in the formula and interfere with the surface processing detection, the fourth, sixth, and eighth orders are used to describe the surface profile. The surface parameters are shown in Table 3:

[0073] Table 3 Even-order aspheric parameters

[0074]

[0075] Since the optical path lengths of light rays corresponding to different positions on the aperture in the off-axis structure are different, the correction lens group also needs appropriate eccentricity and tilt to better correct the wavefront aberration. The eccentricity in the Y direction is -60.1 and the tilt in the X direction is 16.1, and the final image is formed on the digital micromirror device 6.

[0076] The micromirror on the digital micromirror device 6 will be deflected by ±12°, and the corresponding reflected light will also be deflected by ±24°, which means that the object plane and the image plane of the transposed mirror group will be tilted and meet the following Figure 1 The imaging rules shown.

[0077] Depend on Figure 1 As can be seen in (a), if the edge light wants to avoid the edge of the lens, the actual deflection angle is not 24°, but there is only a spare angle of 24°-|u|; therefore, the off-axis two-reflection structure adopted by the present invention can prevent the folded light path of the digital micromirror device 6 from overlapping with the objective lens group. Similarly, during the design, it is necessary to limit the objective lens correction lens 1 3, the objective lens correction lens 2 4, the objective lens correction lens 3 5 and other corrective lenses to avoid collision with the transposed lens group.

[0078] Figure 3 is the transfer function of the optical system of the present invention. It can be seen that the transfer function curve of each field of view is greater than 0.35 at 15lp / mm, which meets the basic requirements of the detection system.

[0079] Figure 4 This is a standard spot diagram of the optical system of the present invention. It can be seen that the overall RMS radius of the diffuse spot of each wavelength and field of view is within the radius of the Airy disk, which can better meet the positioning requirements of the detection system.

[0080] Figure 5 The diffraction circle energy curve of the optical system of the present invention shows that it is basically close to the diffraction limit. The energy within a radius of 30 microns is greater than 75%, which meets the detection energy requirement of the system.

[0081] The high dynamic range infrared asteroid detection optical system based on a digital micromirror device of the present invention modulates the light intensity of the selected area on the image plane by adding a digital micromirror device (DMD) to change the micromirror deflection angle of the selected area during the detection process, thereby realizing high dynamic range detection. At the same time, the front-end imaging objective lens area adopts the form of off-axis two-mirror and correction lens group, realizing the folding of the light path while avoiding the obstruction of the secondary mirror. In addition, the off-axis reflection can make the transposed light path after the digital micromirror device stagger with each other while having a larger entrance pupil diameter, avoiding interference between the optical elements, improving the rationality of the system, and reducing the envelope volume of the system.

[0082] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A high dynamic range infrared asteroid detection optical system based on digital micromirror devices, characterized in that: It comprises: an objective lens group, a digital micromirror device (6), a transposition lens group, an exit pupil (12) and an image plane (13) which are arranged in sequence in the direction of the optical path; in: The objective lens group comprises: a primary reflector (1), a secondary reflector (2) and a correction lens group; the primary reflector (1) and the secondary reflector (2) are off-axis double-reflector structures; the correction lens group is used to expand the field of view and balance the aberration; The function of the digital micromirror device (6) is to achieve high dynamic range detection of asteroids; The function of the transposition mirror group is to eliminate the residual aberration of the objective lens and the aberration introduced by the digital micromirror device (6) while performing secondary imaging; The exit pupil (12) is the exit pupil of the transposed mirror assembly; The image plane (13) is the final imaging position.

2. The high dynamic range infrared asteroid detection optical system based on digital micromirror device according to claim 1, characterized in that: The structure of the exit pupil (12) matches the cold screen.

3. The high dynamic range infrared asteroid detection optical system based on digital micromirror device according to claim 1, characterized in that: The surface of the main reflector (1) is a free-form surface, and the surface sag of the main reflector (1) is defined as: Among them, r 2 =x 2 +y 2 is a polar coordinate variable; is the paraxial curvature, R0 is the radius of curvature of the surface at that location; k is the cone coefficient; N is the total number of polynomial coefficients in the series; A i is the coefficient of the i-th expanded polynomial, which is just a power series in the x and y directions.

4. The high dynamic range infrared asteroid detection optical system based on digital micromirror device according to claim 1, characterized in that: The surface of the secondary reflector (2) is an even-order aspheric surface, and the surface sag of the secondary reflector (2) is defined as: Among them, r 2 =x 2 +y 2 is a polar coordinate variable; is the paraxial curvature, R0 is the surface curvature radius; k is the cone coefficient; α i are the coefficients of the higher-order terms.

5. The high dynamic range infrared asteroid detection optical system based on digital micromirror device according to claim 1, characterized in that: The correction lens group includes: objective correction lens one (3), objective correction lens two (4) and objective correction lens three (5); The surface of the objective lens correction lens 1 (3) is an even-order aspheric surface; The surface shapes of objective lens correction lens 2 (4) and objective lens correction lens 3 (5) are standard spherical lenses; The surface sag of the objective lens correction lens (3) is defined as: Among them, r 2 =x 2 +y 2 is a polar coordinate variable; is the paraxial curvature, R0 is the surface curvature radius; k is the cone coefficient; α i are the coefficients of the higher-order terms.

6. The high dynamic range infrared asteroid detection optical system based on digital micromirror device according to claim 1, characterized in that: The transfer lens group includes: a transfer lens group lens 1 (7), a transfer lens group lens 2 (8), a transfer lens group lens 3 (9), a transfer lens group lens 4 (10) and a transfer lens group lens 5 (11); The surface shapes of the transfer lens group lens 1 (7), the transfer lens group lens 2 (8), the transfer lens group lens 3 (9), the transfer lens group lens 4 (10) and the transfer lens group lens 5 (11) are standard spherical lenses.

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