JP2019090890A - Imaging optical system and imaging apparatus - Google Patents

Abstract

To provide a compact variable power optical system.SOLUTION: There is provided an imaging optical system 6 including: a reflection optical system 10 with a positive refractive power; and a refractive optical system 20 with a positive refractive power located on an image surface side of the reflection optical system, in ascending order of the distance from an object side 2. The reflection optical system 10 includes: a main mirror M1 with a recessed surface facing the object side 2; and a sub mirror M2 on the optical axis of the main mirror for guiding light reflected to the main mirror to the image surface side. The refractive optical system 20 includes: a first lens group G1, which moves integrally with the reflection optical system at the time of zooming and moves alone at the time of focusing; and a second lens group G2, which moves alone at the time of zooming, in ascending order of the distance from the object side 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging optical system including a reflection optical system and an imaging apparatus.

  Patent Document 1 describes that a compact catadioptric optical system is provided. This catadioptric optical system, in order from the object side, has a first lens group of positive refracting power and a second lens group of positive refracting power having a main reflecting mirror and a sub mirror to form a primary image of an object. It has an objective optical system, and an eyepiece optical system that forms an exit pupil with light from this primary image.

Japanese Patent Application Laid-Open No. 06-273674

  There is a need for a compact imaging optical system including a reflection optical system, capable of zooming, and further capable of easily realizing a focusing mechanism.

  One embodiment of the present invention includes, in order from an object side, a reflective optical system having positive refractive power, and an imaging having a refractive optical system having positive refractive power for imaging light guided to the image plane side by the reflective optical system. It is an optical system. The reflective optical system includes a main mirror having a concave surface facing the object side, and a sub mirror disposed on the optical axis of the main mirror and guiding light reflected by the main mirror to the image plane side. The dioptric system moves integrally with the catoptric system during zooming in order from the object side, and moves independently during the zooming from the first lens group which moves independently during focusing. And the lens group of

  An imaging optical system in which a reflection optical system is disposed on the object side can replace a lens with a large aperture on the object side with a reflection optical system, so that the price of the lens can be suppressed. It is suitable for an imaging optical system. In addition, the entire length of the imaging optical system can be shortened. There is also an advantage that a small bright optical system can be provided. In the present invention, the imaging optical system is divided into a reflective optical system disposed on the object side and a dioptric optical system disposed on the image plane side, whereby the reflective optical system is provided during zooming and focusing. And dioptric optical system can be easily divided and controlled. On the other hand, various aberrations in zooming are corrected by moving the first lens unit disposed closest to the side of the reflective optical system integrally with the reflective optical system during zooming, and an image of the reflective optical system is further corrected. By performing focusing with the first lens group disposed on the surface side, it is possible to provide an inner focus type imaging optical system including a reflection optical system.

The combined focal length fm of the reflective optical system and the combined focal length fa from the telephoto end to the wide angle end of the imaging optical system may satisfy the following conditions.
10 <fm / fa <20 (1)
Below the lower limit, the power of the reflective optical system becomes too strong and aberration correction becomes difficult, and when the upper limit is exceeded, the power of the reflective optical system becomes too small and the total length of the imaging optical system becomes long.

  The second lens group of the refractive optical system may include a front group of negative power which moves independently during zooming and a rear group of positive power which moves independently during zooming. . The lens constituting the refractive optical system may be made of germanium or chalcogenide.

  One of the other aspects of this invention is an imaging device which has an imaging optical system as described above, and an imaging device arrange | positioned at the image surface side of an imaging optical system.

FIG. 2 is a diagram showing a configuration of an imaging apparatus including an imaging optical system. The figure which shows lens data. The figure which shows an aspheric coefficient. The figure which shows zoom data. The figure which shows various values.

  FIG. 1 shows an example of an imaging apparatus (camera, camera apparatus) provided with an optical system for imaging. FIG. 1 (a) shows the arrangement at the wide-angle end, and FIG. 1 (b) shows the arrangement at the telephoto end. The imaging apparatus 1 includes an imaging optical system (imaging optical system, lens system) 6 and an imaging element (imaging device) disposed on the image plane side (image side, imaging side, imaging side) 3 of the imaging optical system 6 , Image plane 5). The imaging device 5 is adjusted so as to obtain an infrared (infrared) image, and the imaging device 1 is an infrared imaging device such as a thermal imaging system or a monitoring application. The imaging optical system 6 is a telephoto zoom lens system for infrared light.

  The imaging optical system 6 includes, in order from the object side 2, a reflective optical system 10 of positive refractive power and a refractive optical system 20 of positive refractive power disposed on the image plane side 3 of the reflective optical system 10. The reflective optical system 10 has a function as an objective lens for condensing light from the object side (subject side) 2, and the dioptric optical system 20 images the light guided to the image plane side 3 by the reflective optical system 10. It includes a function of forming an image on the imaging device 5 which is a plane.

  The reflective optical system 10 is disposed on the optical axis 7 of the main mirror M1 of positive power having a concave surface facing the object side 2 and the optical axis 7 of the main mirror M1, and guides the light reflected by the main mirror M1 to the image plane side And a negative power submirror M2 having a convex surface on the image plane side 3. In this reflection optical system 10, the sub mirror M2 reflects light along the optical axis 7, and on the image plane side 3 of the main mirror M1, to the dioptric system 20 coaxially arranged with the optical axis 7 Lead.

  The dioptric system 20 moves sequentially from the object side 2 integrally with the catoptric system 10 during zooming, and independently during the zooming with a first lens group G1 moving independently during focusing. And a moving second lens group G2. The second lens group G2 further includes a front group G2f of negative refractive power which moves independently during zooming, and a rear group G2b of positive refractive power which moves independently during zooming.

  The reflective optical system 10 on the most object side 2 and the first lens group G1 as a whole constitute a moving group of positive power, and move to the object side 2 when zooming from the wide angle end to the telephoto end. The front group G2f forms a moving group of negative power as a whole, and moves to the image plane side 3 when zooming from the wide-angle end to the telephoto end. The rear group G2b as a whole constitutes a moving group of positive power, and moves to the image plane side 3 when zooming from the wide-angle end to the telephoto end.

  In the refractive optical system 20 of this embodiment, the first lens group G1 is a single-plate configuration of a biconvex positive lens L1 made of germanium. The front group G2f of the second lens group G2 has a two-lens configuration of a negative meniscus lens L2 made of chalcogenide and convex on the image plane side 3 and a positive meniscus lens L3 made of germanium and convex on the image plane side 3 is there. The rear group G2b of the second lens group G2 is a single-element configuration of a positive meniscus lens L4 made of chalcogenide and convex on the object side 2.

  FIG. 2 shows data of each optical element (mirror and lens) constituting the imaging optical system 6. The radius of curvature (Ri) is the radius of curvature (mm) of each surface (S) of each optical element arranged in order from the object side 2, and the surface spacing di is the distance (mm) along the optical axis between the surfaces, the refractive index nd indicates the refractive index (wavelength 11 μm) of each lens and the focal length (wavelength 11 μm) of each lens.

The surface S1 of the main mirror M1, the surface S2 of the sub mirror M2, the surface S3 of the object side 2 of the lens L1, the surface S6 of the image surface 3 of the lens L2, the surface S8 of the image surface 3 of the lens L3, an object of the lens L4 The surface S9 of side 2 is aspheric, and the aspheric coefficients are shown in FIGS. 3 (a) and 3 (b). The aspheric surface is shown in FIGS. 3A and 3B, where X is the coordinate in the optical axis direction, Y is the coordinate in the direction perpendicular to the optical axis, the traveling direction of light is positive, and R is the paraxial radius of curvature. It is expressed by the following equation using coefficients K, A, B, C, D and E. "En" means "10 to the n-th power".
X = (1 / R) Y2 / [1+ {1- (1 + K) (1 / R) 2Y2} 1/2]
+ AY 4 + BY 6 + CY 8 + DY 10 + EY 12

  FIG. 4 shows values of the surface intervals V1, V2, and V3 of the groups G1, G2 f, and G2 b, and the imaging device 5, which move during zooming. FIG. 5 shows various values of the imaging optical system 6. The imaging optical system 6 is a zoom optical system (variable magnification optical system) having a magnification change ratio of 1.5, and an F number (FNo.) Is 1.4 at the wide angle end and 2.1 at the telephoto end. It is a variable power optical system 6 for bright infrared rays, which is 2.5 or less from the end to the telephoto end. In addition, the distance on the optical axis from the surface S2 of the secondary mirror M2 to the imaging surface of the imaging device 5 is 227 mm at the wide angle end and 241 mm at the telephoto end. It is a system 6

  The combined focal length fm of the reflective optical system 10 is 3725 mm, and the combined focal length fa of the whole system of the imaging optical system 6 is 200.0 mm at the wide angle end and 299.9 mm at the telephoto end, and fm / fa is a wide angle 18.63 at the end and 12.42 at the telephoto end, satisfying the condition (1). Accordingly, it is possible to provide the infrared imaging optical system 6 which is compact and has good correction of various aberrations.

  In this imaging optical system 6, a reflection optical system 10 is disposed on the object side 2, and a focusing optical system that has a large aperture on the object side 2 is replaced with a reflection optical system instead of a lens. Therefore, it is possible to omit the large aperture lens on the object side 2 which is one of the factors of high cost in the infrared optical system, and the FNo. Can provide a bright and bright infrared optical system. In particular, the total length of the reflective optical system 10 is shortened by making the reflective optical system 10 a Cassegrain-type optical system by combining the primary mirror M1 of positive power and the secondary mirror M2 of negative power facing the primary mirror M1. A compact imaging optical system 6 is realized as a whole.

  Furthermore, the catoptric system 10 is disposed on the object side 2, the dioptric system 20 is disposed on the image plane side 3, and the first lens group G 1 on the most object side 2 of the dioptric system 20 is zoomed. By moving integrally with the system 10, the first lens group G1 is moved during focusing to realize the inner focus. Therefore, aberration correction can be performed by including the first lens group G1 without configuring the moving group that moves during zooming with the reflective optical system 10 alone, and the first lens group G1 can be used as the reflective optical system. The inner focus is realized by a simple mechanism by separating from the main mirror M1 to the image plane side 3 rather than inside the system 10.

  Further, the refractive optical system 20 has a four-lens configuration, and from the object side 2, a lens L1 made of germanium, a lens L2 made of chalcogenide, a lens L3 made of germanium and a lens L4 made of chalcogenide are disposed. Germanium glass is a lens material having a transmission wavelength band in the infrared region of 2 to 20 μm, a high refractive index of around 4.0, and particularly low dispersion characteristics in the vicinity of the wavelength band of 3 to 12 μm. Chalcogenide glass, on the other hand, is a lens material that has high infrared transparency, a lower refractive index, and a higher dispersion than germanium lenses. By alternately arranging lenses different in refractive index and dispersion with respect to infrared rays, it is possible to provide an imaging optical system 6 for infrared rays whose chromatic aberration is well corrected. In particular, the front group G2f of the second lens group G2 is a combination of a lens L2 made of chalcogenide of negative power and a germanium lens L3 of positive power, which is a combined movement of meniscus lenses directed in the same direction It is a group and works well for correcting chromatic aberration during zooming.

  In addition, the first lens group G1 to which the light output from the reflective optical system 10 is first input is a lens for inner focusing, and furthermore, by adopting a lens L1 made of germanium having a high refractive index. The focus adjustment function is enhanced. In addition, the three moving groups of the refractive optical system 20, that is, the front group G2f and the rear group G2b of the first lens group G1 and the second lens group G2 have a symmetrical power arrangement of positive-negative-positive. And a power arrangement suitable for aberration correction.

  In the above, the present invention is described using an imaging device for infrared (infrared light) provided with a lens made of germanium and a lens made of chalcogenide as an example, but for infrared light, a lens made of silicon A lens made of ZnS or the like may be employed, or a combination of the reflective optical system 10 and the refractive optical system 20 for visible light may be used.

Reference Signs List 1 imaging device, 6 imaging optical system 10 reflective optical system, 20 refractive optical system

Claims (5)

From the object side, a reflective optical system of positive refractive power,
And a refractive optical system of positive refractive power disposed on the image plane side of the reflective optical system,
The reflective optical system includes a main mirror having a concave surface facing the object side;
And a secondary mirror disposed on the optical axis of the primary mirror to guide the light reflected by the primary mirror to the image plane side,
The refracting optical system moves in order from the object side, integrally with the reflective optical system during zooming, and a first lens group which moves independently during focusing.
An imaging optical system including a second lens group which moves independently during zooming; In claim 1,
An imaging optical system in which a combined focal length fm of the reflection optical system and a combined focal length fa from the telephoto end to the wide angle end of the imaging optical system satisfy the following condition;
10 <fm / fa <20 In claim 1 or 2,
The second lens group comprises a front group of negative refractive power which moves independently during zooming;
An imaging optical system including a rear lens of positive refractive power which moves independently during zooming. In any one of claims 1 to 3,
An imaging optical system, wherein a lens constituting the refractive optical system is made of germanium or chalcogenide. An imaging optical system according to any one of claims 1 to 4.
And an imaging device disposed on the image plane side of the imaging optical system.

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