JPS602647B2 - Catadioptric optical system that can be switched to a pure refractive lens system - Google Patents

Description

[Detailed description of the invention] The present invention relates to a lens system with variable focal length.

The method of changing the focal length of a photographic lens is as follows:
Methods such as a method of changing lenses, a method of adding a conversion lens, etc. are known, but interchangeable lenses and conversion lenses are large in volume and weight and are inconvenient to carry. Another well-known lens is a zoom lens, but it is complicated and expensive. On the other hand, as a type of telephoto lens system, the catadioptric optical system using a reflector has traditionally been popular, but this is only known as a type of interchangeable lens without variable focal length. there were.

An object of the present invention is to provide a simple variable focal length lens system based on the above catadioptric optical system.

In order to achieve the above object, the present invention is characterized in that in a catadioptric optical system, the secondary mirror that obstructs the light rays entering from the center is configured to be selectively moved out of the optical path. be.

As a result, when the secondary mirror is in the optical path, it can be used as a secondary catadioptric optical system, and when the secondary mirror is moved out of the optical path, it reflects and refracts the light incident from the center. It is possible to form an image only through the lens system and use it as a lens system with a shorter focal length than the above. The present invention will be explained below based on the illustrated embodiments. FIG. 1 shows a first embodiment of the present invention. 1 is protective glass, 2
is a meniscus-type back-reflection primary mirror having a concave reflective surface 2a facing the object side and a light transmitting portion 2b in the center.

Reference numeral 3 denotes a meniscus-type back-reflection secondary mirror having a convex reflection surface 3a facing the side image for reflecting light from the primary mirror.

4 is a refractive lens system located closer to the object than the secondary mirror.
When used as a Nagakuraba point lens system, the secondary mirror is placed at the position indicated by the broken line in Figure 1, and light incident from the periphery is formed into an image only by the reflection system. In this case, the optical system is exactly the same as the conventional catadioptric optical system, and the refractive lens system 4 does not participate in image formation. When used as a short focal length lens, the secondary mirror 3 is moved out of the optical path. In this case, the light incident from the central portion passes through the light transmitting portion 2b of the primary mirror and is formed into an image by the refractive lens system 4 only. When removing the secondary mirror 3, the secondary mirror 3 may be separated from the lens barrel and removed, or the secondary mirror can be raised to be movable inside the lens barrel, and the position within the optical path and outside the optical path can be changed by external operation. You may switch between the positions. FIG. 2 shows a second embodiment of the invention.

Parts common to those in FIG. 1 are given the same reference numerals. The characteristics of this embodiment are that the primary mirror 2 and the secondary mirror 3 constitute an afocal system, and that the refractive lens system 4
is located within the light transmitting portion 2b of the primary mirror 2 and is also involved in image formation as a catadioptric optical system. The primary and secondary mirrors are surface reflective. In this embodiment, when the secondary mirror 3 is removed, the light incident from the center is imaged only by the refractive lens system 4, so that it can be used as a short focal length lens. When the secondary mirror 3 is in the optical path, the incident light from the periphery is formed into an image, but in this case, the same effect as placing a conversion lens made of an afocal system in front of the refractive lens system 4 can be obtained. This makes the lens as a whole a long focal length lens. FIG. 3 shows a third embodiment of the present invention.

In this embodiment, a correcting lens 5 having a convex surface facing the object side is used instead of the protective glass. The primary mirror 2 has a negative varnish lens as a whole, and the periphery of the image side surface is used as a reflective surface 2a to form a concave reflective surface facing the object side. The central light transmitting portion 2b has negative refractive power. When used as a long focus lens, the refractive lens system 4 is moved out of the optical path, and the light incident from the periphery is focused by the correcting lens 5, the primary mirror 2, the secondary mirror 3, and the light transmitting part 2b of the primary mirror. I can imagine it. When used as a short focus lens, the secondary mirror 3 is moved out of the optical path, and the refractive lens system 4 is inserted in its place at the position shown. Therefore, light from the central portion is formed into an image by the correcting lens 5, the refractive lens system 4, and the light transmitting portion 2b of the primary mirror. In this embodiment as well, the secondary mirror 3 and the refractive optical system may be separated from the mirror 8 and inserted alternately, or they may be movably built in and switched by external operation. FIG. 4 shows a fourth embodiment of the present invention, which basically has the same configuration as the third embodiment.

That is, when used as a long focal length lens, image formation is performed by the correct lens L, the primary mirror M, the secondary mirror M2, the light transmitting portion L2 of the primary mirror, and the lens systems L3 and L4. When used as a short focus lens, the refractive lens system L,',L2'
, L3', a light transmitting portion of the primary mirror, and lens systems L3 and L4 form an image. In the above-mentioned use, the entire refractive lens system L, ', L2', S' and the secondary mirror M2 are configured to be separable from the lens barrel, and the lens mirror 8
Alternatively, the lens L3' of the refractive lens system and the secondary mirror M2 may be configured to be movable inside the lens mirror Tsukioka, and can be switched into the optical path by external operation. You can also insert it. The refractive lens system inserted alternately with the secondary mirror into the optical path may be a part of the refractive lens system that participates only in image formation as a short focal length lens. Table 1 below shows the data of the fourth example. Table I.
0 FNo-6.8 Radius of curvature Core thickness Refractive index Abbe number (part involved in image formation as a short focus lens) 30.74 Nishima 8 Parts involved in image formation) f 〒 Reibi Raku passing diameter F So C Nikishi 8 Refraction brush? Figure 5.
FIG. 6 is an aberration diagram in the case of a long focal length lens and a short focal length lens, respectively, in the fourth embodiment.

FIG. 7 shows a fifth embodiment of the present invention, which basically has the same configuration as the first embodiment.

That is, when used as a short focus lens, the secondary mirror M2 is moved out of the optical path. Table 2 below shows the data of the fifth example. Table 2 (Parts involved in image formation as a long focal length lens) f〒75
．． 0 FNo=4.0 2=15 56'
Radius of curvature Core thickness Refractive index Abbe number (part involved in image formation as a short focus lens) f = 50〇 F
No=4.0 2=23 44' radius of curvature
Core thickness Refractive index Abbe number (portion involved in image formation as a short focus lens) f=50.0 FNo=
4.0 2:2zu 4 and 1' curvature Mikasamine
Core thickness Abbe number Abbe's number Figures 8 and 9 are aberration diagrams in the case of a long focus lens and a short-circuit point lens, respectively, in the fifth embodiment.

As is clear from the above, according to the present invention, a variable focal length lens system is constructed with a very simple configuration.

In the present invention, the volume of the secondary mirror that is moved out of the optical path is much smaller than that of a mirror mirror, and even if it is separated from the lens barrel, it is more convenient to carry than an interchangeable lens or a conversion lens. , if it is switchably built into the lens barrel, the entire lens can be used as a single variable focal length lens. In addition, as a long focal length lens, the advantages of the catadioptric optical system, such as short overall length and low chromatic aberration, are fully utilized, and it can also be used in conventional catadioptric optical systems. The light beam that enters from the center, which was not present, is used for imaging as a short focus lens, and the lens system as a whole has a streamlined design.

[Brief explanation of the drawing]

FIG. 1 is a schematic lens configuration diagram of the first embodiment of the present invention, FIG. 2 is a schematic lens configuration diagram of the second embodiment, and FIG. 3 is a schematic lens configuration diagram of the second embodiment.
A vague lens configuration diagram of the embodiment, FIG. 4 is a lens configuration diagram of the fourth embodiment, FIGS. 5 and 6 are aberration diagrams of the fourth embodiment, and FIG. 7 is a lens configuration diagram of the fifth embodiment. 8 and 9 are aberration diagrams of the fifth embodiment. 2,M,...Primary mirror, 3,M2...Secondary mirror, 4,L
', L2', L3'... Refractive lens system. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure T Figure 8 Figure 9

Claims (1)

[Claims] 1 A catadiopter that includes a primary mirror that has a reflective surface facing the object side and a light transmitting part in the center, and a secondary mirror that is located on the object side of the primary mirror and has a reflective surface that faces the image side. In the trick optical system, a reflective telephoto lens is configured with the secondary mirror positioned within the optical path, and the secondary mirror is moved out of the optical path, and light incident from the center of the lens system is imaged by a refractive lens system. A catadioptric optical system for a variable focal length photographic lens that can also be used as a purely refractive lens system with a shorter focal length than the reflective telephoto lens.