JPH05288908A - Optical system - Google Patents

Abstract

(57) [Summary] The optical system of the present invention is an optical system including a reflecting mirror and a holding member for holding the reflecting mirror, such as an afocal optical system. It is made of a material having a coefficient of thermal expansion. [Effect] The optical system having the above-described structure can exert desired optical performance without heat control even in a severe thermal environment such as a space environment, and can downsize the entire apparatus. In addition, the device can be prevented from becoming complicated.

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system capable of compensating for thermal effects such as a telescope and a beam shaping optical system.

[0002]

2. Description of the Related Art In general, optical telescopes and beam shaping optical systems are required to have high imaging performance and transmitted wavefront characteristics. Especially, in the reflective optical system, the environmental performance, especially the deformation of the mirror and the supporting structure due to heat has a great influence on the optical performance. Therefore, in the past, in order to prevent deformation due to heat, <a> use a low thermal expansion material for the mirror, <b> perform temperature control of the entire optical system,
C> Measures such as using an active alignment mechanism of mirrors are taken.

However, the measure <a> against the deformation due to heat deteriorates the optical performance due to the influence of the supporting structure other than the mirror. In addition, the measure <b> has a problem that the size of the temperature control device becomes large as the size of the optical system becomes large, and as a result, the size of the entire device becomes large. further,
With the measure <C>, the device becomes complicated, and there is a problem in reliability particularly in long-term use in outer space.

[0004]

As described above, in the conventional optical system, the countermeasures <a>, <b>, and <c> which are taken to prevent the deformation due to heat have their own drawbacks. have.

The present invention has been made in consideration of the above circumstances, and solves the technical problem of the above-mentioned conventional optical system and can compensate the thermal effect without temperature control. The purpose is to provide. [Constitution of Invention]

[0006]

The optical system of the present invention has a plurality of reflecting mirrors and a holding device for holding these reflecting mirrors, such as an afocal optical system (afocal optical system) having a light-collecting power of zero. In the optical system including members, the reflecting mirror and the holding member are made of materials having substantially the same thermal expansion coefficient.

[0007]

The optical system having the above-described structure can achieve desired optical performance without heat control even in a severe thermal environment such as space environment, and can downsize the entire apparatus. In addition, the device can be prevented from becoming complicated.

[0008]

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the optical system of this embodiment. This optical system is composed of a main mirror 1 having a center radius rotational parabola having a center curvature radius R1 or a rotationally higher-order aspherical surface based on the rotation paraboloid, and a center curvature radius formed of the same material as the main mirror 1. A secondary mirror 2 having a central radius rotational parabola of R2 or a rotational higher-order aspherical surface based on the rotational paraboloid, and a primary mirror 1 that holds the primary mirror 1 so as to share the same optical axis 3 and Secondary mirror 2
And a rod-shaped sub-mirror radially arranged in a plurality of equal parts for supporting and fixing the sub-mirror 2 so as to share the optical axis 3 with the lens-barrel 4. It consists of a support 5. The primary mirror 1 and the secondary mirror 2 are arranged at positions sharing the focal point F, and form a so-called confocal afocal optical system (afocal optical system) having a zero focusing power. Further, a through hole 6 is provided in the central portion of the primary mirror 1,
The light beam 7 reflected by the secondary mirror 2 is made to pass through. Next, the operation of the optical system having the above configuration will be described.

The thermal expansion coefficient of the material forming the primary mirror 1, the secondary mirror 2, the lens barrel 4 and the secondary mirror support 5 is α (unit: 1 /
K). Here, the distance between the primary mirror 1 and the secondary mirror 2 is L. Now, if a uniform temperature change of ΔT (unit: K) occurs in the entire optical system, the distance between the primary mirror 1 and the secondary mirror 2 is L ′.
= L (1 + αΔt). On the other hand, the central curvature radius R1 of the primary mirror 1 due to the thermal expansion is R1 ′ = R1 (1 + αΔt). Further, the center curvature radius R2 due to the thermal expansion of the secondary mirror 2
Is R2 ′ = R2 (1 + αΔt). Here, when a rotating high-order aspherical surface based on a paraboloid of revolution is used for the primary mirror 1, there is an influence of a higher-order term, but this is negligible and can be ignored. In general, in a confocal afocal optical system, the following expression (1) must be satisfied in order to realize on-axis aberration-free. Rl = R1 / 2 · (1 + R2 / R1) ……… (1)

In the equation (1), L ', R1', R2 '
By substituting, the equation (1) is obtained again. This is
Equation (1) also shows that it holds for L ′, R1 ′, and R2 ′. In other words, the primary mirror 1, the secondary mirror 2,
By forming the lens barrel 4 and the sub-mirror support 5 from the same material, it means that axial aberration-free can be realized without thermal control. This is true not only in the parabolic-parabolic optical system, but also in the higher-order aspherical optical system with axial aberration.

As described above, in the optical system of this embodiment, the primary mirror 1, the secondary mirror 2, the lens barrel 4 and the secondary mirror support 5 are made of the same material, so that they can be used in severe thermal environments such as space environments. Also, desired optical performance can be exhibited without thermal control. Moreover, not only can the entire apparatus be downsized, but the apparatus can be prevented from becoming complicated.

In the above embodiment, the primary mirror 1, the secondary mirror 2, the lens barrel 4 and the secondary mirror support 5 are made of the same material so that the thermal expansion coefficients of these members are equalized. If the material has a substantially constant thermal expansion coefficient, different materials may be combined to form the optical system. Further, materials having different thermal expansion coefficients may be combined so as to be close to the thermal expansion coefficients of the primary mirror and the secondary mirror. Further, although the afocal optical system is illustrated in the above embodiment, the present invention is also applicable to an image forming optical system for focusing. Further, in the above-mentioned embodiment, the reflection type optical system is exemplified, but it is also applicable to the catadioptric type optical system.

[0014]

The optical system of the present invention is an optical system comprising a reflecting mirror and a holding member for holding the reflecting mirror, such as an afocal optical system. The reflecting mirror and the holding member have substantially the same coefficient of thermal expansion. Made of the following materials,
Even in severe thermal environments such as space environments, without thermal control,
A desired optical performance can be exhibited. Moreover, not only can the entire apparatus be downsized, but the apparatus can be prevented from becoming complicated.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an entire optical system of an embodiment of the present invention.

[Explanation of symbols]

 1: primary mirror, 2: secondary mirror, 4: lens barrel, 5: secondary mirror support.

Claims (2)

[Claims] 1. An optical system comprising a reflecting mirror and a holding member for holding the reflecting mirror, wherein the reflecting mirror and the holding member are made of materials having substantially the same thermal expansion coefficient. 2. The optical system constitutes an afocal optical system comprising a plurality of reflecting mirrors and a holding member for holding these reflecting mirrors, and the plurality of reflecting mirrors and the holding member have substantially the same thermal expansion. The optical system according to claim 1, wherein the optical system is made of a material having a coefficient.