# Design of Parabolic Off-Axis Reflector Optical System for Large Aperture Single Star Simulators
## 4 Parabolic Off-Axis Reflective Optical System Design
### Optical System Stray Light Suppression  
The optical system of a large aperture single star simulator is different from the imaging system, and its stray light mainly originates from the multiple scattering inside the system, i.e., the perturbation of endogenous stray light. Through the analysis, we use in the optical system set up stray light suppression diaphragm as well as the box inside and isolation platform and other blackening treatments to suppress the system stray light. According to the results of the optical system design, the distance L from the small aperture to the first face of the objective lens is 973 mm, the secondary mirror aperture is \(\Phi\)255 mm, the radius tensor angle of the objective lens to the small aperture is about 2.94\({}^{\circ}\). The radius angle of the beam exiting the small aperture is about 90\({}^{\circ}\), and many non-imaging beams exist in the optical system. In order to avoid non-imaging beams in the optical system scattering light out of the objective lens, it is necessary to set the aperture in the optical system stray light suppression diaphragm. Stray light suppression diaphragm through the size of the aperture to not block the imaging beam shall prevail, as shown in Figure 11, but the aperture diaphragm can have a sound effect; the location of the determination is critical. If the stray light suppression diaphragm is located in position b or further away from the small aperture plate in Figure 11, there will be diffuse reflection in the main direction of light through the stray light suppression diaphragm into the back of the system; if the stray light suppression diaphragm is located in Figure 2, between a, b, the diffuse reflection in the main direction of light will not be transmitted through the stray light suppression diaphragm, but a diffuse reflection of the second direction of the light is still able to pass through the stray light suppression diaphragm (shown by dotted lines in the figure). If the stray light suppression diaphragm is located in position a or closer to the small aperture plate, then a diffusely reflected light will not pass through the stray light suppression diaphragm, and the second diffuse reflection occurs in the wall of the optical system, so that in the stray light through the stray light suppression diaphragm before it has been many times before the attenuation, so the stray light suppression diaphragm can be located in position a. The distance from the star point plate to the stray light suppression diaphragm is calculated as shown in Equation (10). \[\left\{ \begin{array}{l}\tan\alpha=\frac{d}{2\zeta_{0}}\\ \tan\beta=\frac{D}{2\zeta_{0}}\end{array} \right. \tag{10}\]  
Figure 11: Non-imaging beam suppression. \begin{table}
\begin{tabular}{c c} \hline \hline
**Evaluation Parameter** & **Value** \\ \hline
98\% Monte Carlo analysis of MTF values & \textgreater{}0.6966 \\
90\% Monte Carlo analysis of MTF values & \textgreater{}0.7113 \\
80\% Monte Carlo analysis of MTF values & \textgreater{}0.7193 \\
50\% Monte Carlo analysis of MTF values & \textgreater{}0.7302 \\
20\% Monte Carlo analysis of MTF values & \textgreater{}0.7372 \\
10\% Monte Carlo analysis of MTF values & \textgreater{}0.7396 \\
2\% Monte Carlo analysis of MTF values & \textgreater{}0.7418 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Tolerance analysis results of optical system. where \(d\) is the aperture of the secondary mirror, \(D\) is the aperture of the light source edge light and is the distance from the star point plate to the stray light suppression diaphragm.