CN101672978A - Catadioptric type off-axis three-reflector long-wave infrared optical system - Google Patents

Abstract

The invention discloses a catadioptric off-axis three-reflection long-wave infrared optical system for space-borne or airborne observation of the ground. An optical system composed of a reverse system and a zoom lens group 4. Among them, the off-axis three-mirror can improve the imaging, and its focal length is longer than that of the system. The variable magnification lens group itself is achromatic, and its magnification is 0.35≤β≤1, which shortens the focal length of the off-axis three mirrors and increases the relative aperture of the system. The structure is simple, and is mainly used in long-wave infrared cameras in airborne or spaceborne ground imaging instruments.

Description

A catadioptric off-axis three reflection long-wave infrared optical system

technical field

The present invention relates to optical elements and systems, in particular to a catadioptric off-axis three-reflection, large field of view, and large relative aperture long-wave infrared optical system used in an airborne or spaceborne ground observation imager.

Background technique

In the long-wave infrared imaging optical system, the full transmission system is restricted by the optical material, and the general aperture is below Φ200mm. The catadioptric system generally adopts the structure of two coaxial mirrors plus a correction lens group. This structure has a central occlusion, which reduces the MTF of the system, and is not suitable for applications with a large field of view. With the increase of the relative aperture of the off-axis three-mirror system, its processing and assembly difficulty also increases.

In aerospace remote sensing applications, the reflective telescope system is generally shared in multi-channel cameras, and a field of view separator or color separation device is placed in front of the focal plane of the telescope, which is divided into visible light (VIS), near infrared (NIR), short-wave infrared (SWIR) , Long wave infrared (LWIR) channel. The resolution of the long-wave infrared channel is generally lower than that of the visible near-infrared and short-wave channel. Therefore, the channel is required to have a small focal length and a large relative aperture. When the visible near-infrared is directly used for off-axis three-mirror imaging, the long-wave infrared channel needs to reduce the focal length of the off-axis three-mirror system for perfect imaging.

Contents of the invention

Based on the above problems, the present invention proposes a catadioptric off-axis three reflection long-wave infrared optical system. The purpose of the present invention is to realize an optical system with a large field of view and a large relative aperture by adding a variable magnification lens group behind the off-axis three-mirror system. The range of the magnification of the variable magnification lens group is 0.35≤β≤1, so that a long-wave infrared optical system with a large relative aperture can be obtained from an off-axis three-mirror system with a small relative aperture, and can also be used in a two-speed zoom long-wave infrared system.

The structure of the catadioptric off-axis three-reflection long-wave infrared optical system of the present invention is as shown in Figure 1, and the imaging optical system composed of reflector 1, reflector 2, reflector 3 and variable power lens group 4 in order is characterized in that It lies in: adding the zoom lens group to the traditional off-axis three-mirror system to reduce its focal length and increase its relative aperture, while retaining its advantages of large field of view.

The light beam from the object side passes through the reflector 1 , shoots to the convex reflector 2 , is reflected by the secondary aspheric reflector 3 , and further converges on the image plane 5 with the variable magnification lens 4 .

The catadioptric off-axis three-reflection long-wave infrared optical system must meet the following requirements:

1. The off-axis three-mirror system composed of mirror 1, mirror 2, and mirror 3 can improve imaging.

2. The magnification range of the variable magnification lens group is 0.35≤β≤1.

The biggest feature of the optical system of the present invention is to add a variable power lens group after perfecting the imaging off-axis three-mirror to increase the relative aperture. After ensuring that the off-axis three-mirror can be adjusted independently with visible light, a variable magnification lens group is added to ensure that the difficulty of system installation and adjustment does not increase.

Description of drawings

Figure 1 is a structural diagram of a catadioptric off-axis three-mirror long-wave infrared optical system, wherein: L1 is the distance between the concave mirror 1 and the convex mirror 2; L2 is the distance between the convex mirror 2 and the concave mirror 3; L3 Be the distance between the concave reflector 3 and the variable magnification lens group 4; L4 is the distance between the refracting lens 4-1 and the refracting lens 4-2; L5 is the distance between the refracting lens 4-2 and the refracting lens 4-3; L6 is the distance between the refracting lens 4-3 and the image plane 5; D1 is the distance from the system optical axis of the reflector 1; D2 is the distance from the system optical axis of the reflector 3; Axis distance; α is the angle between the light from the object side and the optical axis of the system; R411 is the radius of curvature of the front surface of the refracting lens 4-1; R412 is the radius of curvature of the rear surface of the refracting lens 4-1; R421 is the front surface of the refracting lens 4-2 Radius of curvature; R422 is the radius of curvature of the rear surface of the refracting lens 4-2; R431 is the radius of curvature of the front surface of the refracting lens 4-3; R432 is the radius of curvature of the rear surface of the refracting lens 4-3.

Fig. 2 is a graph of the optical transfer function of the off-axis three-mirror system in the visible light band (0.48 μm-0.66 μm) in the example.

Fig. 3 is a graph of the optical transfer function of the system at 8.0 μm to 12.0 μm after the off-axis triple mirror plus zoom lens group in the example.

Specific implementation method

According to the optical system structure shown in accompanying drawing 1 among the present invention, we have designed a long wave infrared optical system, technical index is as follows:

Working band: 8.0μm～12.0μm

Diameter: Φ300mm

Field of view: ±2.0° (line field of view)

Off-axis three-mirror F number: F/3.5

System F number: F/1.2

The design results of the specific structural parameters of the system are attached. The optical transfer function curve of the off-axis three-mirror system is shown in Figure 2, and the optical transfer function curve of the system after adding the variable magnification lens group is shown in Figure 3.

Design results of optical structure parameters:

Claims (1)

1. Catadioptric type off-axis three-reflector long-wave infrared optical system, constitute object lens of large relative aperture LONG WAVE INFRARED optical system by concave mirror (1), convex surface reflection (2), concave mirror (3), change convertible lens group (4) successively by object space to the side's of elephant order, it is characterized in that:

A) reflect the big of (2), concave mirror (3) formation by concave mirror (1), convex surface, and can improve imaging alone from the more described refraction-reflection LONG WAVE INFRARED of axle three catoptron F numbers optical system;

B) described change convertible lens group (4) is the achromatic lens group, and lens wherein adopt sphere or non-spherical lens to eliminate aberration;

C) scope that becomes the attainable enlargement ratio of convertible lens group (4) is 0.35≤β≤1;

D) from the light beam process catoptron (1) of object space, directive convex reflecting mirror (2) again by secondary aspherical catoptron (3) reflection, further converges at picture plane (5) with change convertible lens (4).

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