JPH0392809A - Reflection and refraction type optical system - Google Patents

Abstract

PURPOSE:To obtain a large aperture ratio of an about F3.5 and reduce the size of the lens system on the whole and to obtain high optical performance over the entire picture plane by setting respective lens elements of a reflection and a refraction system. CONSTITUTION:The optical system is equipped with a positive lens L1, a refracting concave reflector L2, a refracting reflector L3, a positive lens L4, and a negative lens L5 in order from the object side. Conditions shown by inequalities I - III are satisfied, where (f) is the focal length of the whole system f2 the focal length of the refracting concave reflector L2, f3 the focal length of the lens L1, refracting reflector L3, and the system R11 the radius of curvature of the object-side lens surface of the lens L4, and D2 the interval between the lens L1 and refracting concave reflector L2. Consequently, the large aperture radio and the lens diameter are reduced on the whole and a reflection and refraction optical system having high optical performance is obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a catadioptric optical system using a reflective system and a refractive system, and in particular to a catadioptric optical system that maintains aberration correction well and has an F number of 3.5.
This invention relates to a catadioptric optical system with a large aperture ratio, which is suitable for photographic cameras, video cameras, etc., and which aims to increase the aperture ratio and downsize the entire lens system.

(Prior art) Conventionally, catadioptric optical systems have extremely small chromatic aberrations by using reflective surfaces, and it is easy to correct coma aberration that occurs on reflective surfaces using refractive systems. ratio of the distance from the first lens surface to the image plane)
It is often used in optical systems with long focal lengths because it can make the lens small.

These catadioptric optical systems are, for example,
Publication No. 154, Special Publication No. 43-5951, Special Publication No. 6
This method has been proposed in Japanese Patent Application Laid-open No. 0-18045, Japanese Patent Laid-Open No. 184223-1980, and the like.

However, with catadioptric optical systems, it is generally difficult to increase the aperture ratio and downsize the entire lens system, so in many conventional systems, the aperture ratio has been sacrificed in order to downsize the entire lens system. For example, Japanese Patent Publication No. 60-32853 and Japanese Patent Application Laid-open No. 62-184425 propose catadioptric optical systems in which the overall length of the lens is shortened at the expense of the aperture ratio.

(Problems to be Solved by the Invention) In general, in order to achieve a large aperture ratio in a catadioptric optical system, it is necessary to particularly correct spherical aberration well. In this case, it is preferable to widen the distance between the primary mirror and the secondary mirror in order to properly correct spherical aberration. However, for example,
As proposed in Publication No. 8354, if such a method is used, the total length of the lens will be long compared to the focal length of the entire system (
The problem arises that the telephoto ratio becomes large), the entire lens system becomes large, and the refractive power of the secondary mirror becomes too small compared to the primary mirror, resulting in a short back focus.

In addition, Japanese Patent Publication No. 18354/1983
No. 184223 discloses that a hole is made in the center of the primary mirror and the lens system is supported in this hole.Drilling a hole in the primary mirror is very difficult in terms of processing, and it is also difficult to hold the lens system. was there. In addition, in many cases, catadioptric optical systems have the problem that the secondary mirror produces a large amount of on-axis and off-axis light fluxes, resulting in a decrease in the vignetting light quantity ratio. The present invention maintains an F number of 3.5, a large aperture ratio as a catadioptric optical system, and a predetermined amount of back focus by appropriately setting each lens element of the reflective system and refractive system. The object of the present invention is to provide a catadioptric optical system that is downsized, reduces vignetting of a light beam by a secondary mirror, and has high optical performance over the entire screen.

(Means for Solving the Problems) The catadioptric optical system of the present invention sequentially passes a light beam from an object through a positive lens L1 to a meniscus-shaped lens surface on the image plane side with a concave surface facing the object side. The lens L1 is refracted and reflected toward the object side by a refractive concave reflector L2 whose peripheral portion is a reflective surface M1.
The lens surface on the image side is reflected to the image side by a refractive reflector L3 which is joined to the object side lens surface of the lens L1 and whose object side lens surface is the reflective surface M2. After passing through the central transmission part of the refractive concave reflector L2 through a positive lens L4 whose lens surface is convex and whose image side lens surface is joined to the object side lens surface of the refractive concave reflector L2,
When guiding light to the image plane through a meniscus-shaped negative lens L5 with a concave surface facing the image plane, the focal length of the entire system is f, the focal length of the refractive concave reflector is f2, the lens L1 is Refractive reflection 1! The focal length of the system composed of L3 is f3, the radius of curvature of the object-side lens surface of the lens L4 is R11, and the lens L1 and the refractive concave reflection tl! When the interval of L2 is D2, 2.0 <lf2/f31<2.7...(1)0
．． 1 < D27f <0.2
... (2) 0.01< R11/f <0.3
It is characterized by satisfying the condition (3).

(Example) FIG. 1 and FIG. 2 are lens sectional views of numerical example 1.2 of the present invention, respectively. In the figure, each optical element of the catadioptric system of this embodiment will be explained in the order in which the light beam travels.

LL is a positive lens with both lens surfaces being convex, L2 is a meniscus shape with a concave surface facing the object side, and the peripheral part of the lens surface on the image side is reflective, M1 is a refractor whose center part is a transmitting surface and is used as a primary mirror. A concave reflecting mirror, L3, is a refractive reflecting mirror whose image side lens surface is joined to the object side lens surface of lens L1, and whose object side lens surface (convex surface) is a reflecting surface M2, which is used as a secondary mirror. Both lens surfaces are positive lenses with convex surfaces, and the lens surface on the image side is cemented to the object side lens surface of the refractive concave reflecting mirror L2. L5 is a meniscus-shaped negative lens with a concave surface facing the image plane side.

Incidentally, G1 is a removable filter, and for example, an ND filter with a different density is inserted in place of a diaphragm. G2 is an optical member such as a low-pass filter or an infrared cut filter used in a video camera or the like. Q is an image.

In this embodiment, as shown in the figure, a light beam from an object (not shown) is condensed by a lens L1, and is refracted and reflected toward the object side by a refractive surface of a refractive concave reflector L2 and a reflective surface M1. Next, the light is refracted by the lens L1, reflected toward the object side by the reflective surface M2 of the refractive reflector L3, and then refracted and emitted through the lens L1. After passing through the lens L4, the transmitting surface at the center of the refractive concave reflector L2, and the lens L5 in order,
The light is focused on the image Q and forms an object image.

In this embodiment, each optical element is set as described above, and each optical element is By satisfying the above-mentioned conditional expressions (1) to (3), the catadioptric optical system achieves a large aperture ratio and miniaturization of the entire lens system, and also has high optical performance with little vignetting of the light beam due to the secondary mirror. I am getting .

Next, the technical meaning of each of the above-mentioned conditional expressions will be explained.

Conditional expressions (+) and (2) are intended to reduce the size of the entire lens system and to satisfactorily correct spherical aberration, which is most important when increasing the aperture ratio. In other words, as shown in conditional expression (2), the refractive power of the primary mirror system and the secondary mirror system (
power) is maintained in a well-balanced manner as shown in conditional expression (1), and the overall length of the lens is effectively shortened while ensuring a predetermined back focus.

When the upper limit of conditional expression (1) is exceeded, the back focus increases, but the refractive power of the secondary mirror becomes too strong, resulting in overcorrection of spherical aberration, and the negative Bethespal sum increases, making it impossible to properly correct field curvature. It's getting difficult. Moreover, if the lower limit is exceeded, it becomes difficult to obtain a predetermined amount of back focus while maintaining a large aperture ratio.

If the upper limit of conditional expression (2) is exceeded, it becomes difficult to shorten the overall lens length, and if the lower limit is exceeded, higher-order spherical aberration increases, making it difficult to increase the aperture ratio. .

Conditional expression (3) is used to appropriately set the radius of curvature of the object-side lens surface of lens L4 cemented to primary mirror L2 of the rear refractive lens system that controls the light flux after passing through secondary mirror L3. It is. In other words, since the convergent light reflected by the secondary mirror L3 has spherical aberration and coma aberration corrected in a well-balanced manner, when the central part of the primary mirror is used as a transmissive refractive optical system, the strong refraction of the first lens surface of the primary mirror Due to the concave surface of the force, spherical aberration becomes over-corrected. Therefore, in this embodiment, a positive lens L4 that satisfies conditional expression (3) is arranged on the object side of the primary mirror L2 to satisfactorily correct the overcorrected spherical aberration at this time.

If the upper limit of conditional expression (3) is exceeded, the light beam reflected by the secondary mirror will enter the first lens surface of lens L4 at a large angle of incidence, resulting in overcorrection of spherical aberration, and if the lower limit is exceeded, back focus will occur. This is not good because it becomes too short.

In this example, by satisfying each of these conditional expressions, a catadioptric optical system with a large aperture and a short overall lens length with good aberration correction is achieved. By arranging a negative meniscus lens L5 with a concave surface of strong refractive power facing the image plane side, astigmatism in particular is corrected in a well-balanced manner and the field of view is expanded.

In this embodiment, the lenses L3 and L1 constituting the secondary mirror M2, the lens L4 constituting the rear refractive lens system, and the lens L2 constituting the main fiMl are joined, but even if these are supported separately, the main The purpose of the invention can be achieved. In addition, in this embodiment, the focus is determined by the positive lens L1 and the sub-lens m.
Although it is preferable for aberration correction to be performed by moving both of the M2 laminated lenses, focusing may be performed by moving the entire lens system.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in the order of light progression, Di
is the i-th lens thickness and air spacing in the order of light progression, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens in the order of light propagation, respectively. However, Di assumes that the length measured from the left to the right in the direction of light travel is positive, and the opposite is negative.

Numerical Examples I F-100.0 R 1 inch 364.640 R 2-312.861 R 3- -66.385 R 4- -72.403 (Ml) R 5-
-1i6.385←R3) R6・-3 12. 88 1 (-R2)R 7-
364.640 (-Rl) R8・-45.391 (M2) R9・:l64.640 (-Rl) RIO-312.861 (-82) R11- 1:l. 999 RI2・-68.385 (-R3) 1113・-72.403 (-R4) RI4・ ■ RI5- 0:I RI6- 12.41 [i RI7- 5.595 Rl8- 00 Rl9- ■ FNo.: 1.5 2ω-3.4°D1
・2.703 N I ~ 1.51633 ν
1・64.15D2~15.451 D 3- 2.97:l N 2-1.51633
ν 2~64.15D4~2.973 N3-
1.51633(-N2)υ3-64.15(=ν2)
D5 Seal-15.451 D 6-2.703 N 4-1.51633(-N
l) ν4-64.15 (~νl) D 7-1.622
N 5-1.51633 υ 5-64.15
D 8- 1.622 N 6・1.5163:]
(-N5) ν6-64.15 (1 ν5) D9・2.70
3 N7・1.51633 (-Nl) ν7-64.
15 (1 νI) 010-10.587 DI1- 4.865 N 8-1.5163
3 ν 8・64 l5012- 2.97
3 8 9-1.51633 (-N2) ν9-64.
+5←v2)013・0.541 014−0.541 NIO・1.5+633
ν10-64.15Dl51 0.541 DI6-1.081 Nl!・1.60311
ν]+-60.70DI7- 1.081 018 Stain 3.243 N+2-1.5+6113
ν12嘗64. +5 Conditional expression (1) - 2.2973 (2) - 0.1545 (3)・0.1400 Numerical example 2 F-100.0 R I- 24+. 560 R 2-379.861 R 3- -62.425 R4--69.843 (Ml) R 5- -62.425 (-R3) R 6-37
9.861 (-R2) R 7- 241.560 (-Rl) R8 mouth-44.479 (M2) R 9- 241.560 (-Rl) RIO-379.861 (-R2) Rl+- 11.814 Rl2- -62.425(-R3) R]3- -69.843(-R4) RI4- 12.460 RI5・5.58]? No-3.5 2ω=2.63°D
I-1.622 N]-1.5]633
v I-64.15D 2-17.450 D 3- 1.622 N 2 Maro 1.51633
υ 2-64.15D 4-1.622 8
3-1.51633(-N2)ν3-64.15(-ν
2) D 5-17.450 D 6--1.622 N 4-1.5+633(-
Nl) Z/ 4-64. +5←bl)D 7-1.08
1 N 5-1.51633 ν 5-84.
15D 8” 1.081 N 6-1.51633
(-N5)v6■64. l5(=b5)D 9-1.
622 N 7-1.51533(-Nl)ν7-6
4.15 (1 νl) 010-14.748 DI+- 2.703 N 8-1.51633
υ 8-64.15012- 1.622
N 9-1.5]633←N2)υ 9-64. 1
5 (-υ2)013- 0.541 0141.081 NIO-1.60311
vlo-60.70DI5= 1.081 Rl8- DI6~3.243 NIL-1.51633 ν11 64.15 RI7- Conditional expression (+) ・2368 (2) − 0.1745 (3) − 0.1181 ( Effects of the Invention) According to the present invention, by setting each of the lens elements of the reflective system and the refractive system as described above, it is possible to achieve a large aperture ratio of about 3.5 with an F number of about 3.5, and to reduce the size of the entire lens system. It is possible to achieve a catadioptric optical system with high optical performance over the entire range.

[Brief explanation of drawings]

1 and 2 are lens sectional views of numerical examples 1 and 2 of the present invention, and FIGS. 3 and 4 are various aberration diagrams of numerical example 1.2 of the present invention. In the aberration diagram (A). (B) is the fertilizer magnification β
is when β=0, β-0.064. In the figure, d is the d-line, g is gB, △S is the sagittal image, ΔM
is the Meridian image plane, and Q is the image plane.

Claims (1)

[Scope of Claims] (1) Refraction and concave reflection in which the light flux from the object is sequentially passed through the positive lens L1, with the peripheral part of the meniscus-shaped lens surface on the image side facing the object as the reflection surface M1. A refracting/reflecting mirror L3 which is refracted and reflected toward the object side by a mirror L2, and whose image side lens surface is joined to the object side lens surface of the lens L1 through the lens L1, with the object side lens surface being a reflective surface M2. through the lens L1 and a positive lens L4, both of whose lens surfaces are convex and whose image side lens surface is joined to the object side lens surface of the refractive concave reflector. Reflector L2
After passing through the central transmitting part of the refractive concave reflector, the light is guided to the image plane through a negative meniscus lens L5 with a concave surface facing the image plane. The focal length is f2, the focal length of the system composed of the lens L1 and the refractive reflector L3 is f3, the radius of curvature of the object-side lens surface of the lens L4 is R11, the lens L1 and the refractive concave reflector L
2 is the interval D2, the following conditions are satisfied: 2.0<|f2/f3|<2.7 0.1<D2/f<0.2 0.01<R11/f<0.3 Features a catadioptric optical system.