## 2 Theory and Methods
### Model of the Optomechanical System
#### 2.2.2 Baffle and Vane Design  
For refraction-type optical systems, the usual method to eliminate stray light is to add a baffle and a light-blocking ring. The design of the baffle can effectively suppress the stray light entering the camera lens and block the incident stray light larger than the critical blocking angle. When the scattered and reflected light reaches the inner surface of the baffle, the stray light will generate a halo when it reaches the image surface. In order to  
Figure 3: System tolerance analysis results.  
prevent non-imaging light from reaching the inner surface of the baffle, a light-blocking ring needs to be added at this time.  
The optomechanical structure's ability to suppress stray light increases with the length of the designed baffle. However, in actual engineering applications, the size and weight of the optomechanical system have a certain impact on camera performance. Therefore, the design of the optomechanical structure also needs to be considered. The final design of the baffle needs to be able to block non-imaging light from reaching the detector and at the same time make the effective imaging light smooth enter the imaging surface.  
The three-dimensional model of the camera lens is shown in Figure 4. When the clear aperture of the optical system \(D_{1}=20\) mm, the length of the optical system \(L_{s}=36.76\) mm, the angle of view \(2\beta=28^{\circ}\), the solar evasion angle \(\alpha=30^{\circ}\), and the entrance pupil diameter \(D_{1}=20\) mm are known, the size of the length \(L\) and diameter \(D_{2}\) of the baffle can be calculated by:  
\[\left\{\begin{array}{c}D_{2}=D_{1}+2L\tan\beta\\ L\tan\alpha=D_{1}+L\tan\beta\end{array}\right. \tag{5}\]  
Based on the above equations, \(D_{2}=50.418\) mm, \(L=60.97\) mm, take \(D_{2}=51\) mm, \(L=61\) mm, \(D_{1}=20\) mm, as shown in Figure 5.  
Figure 4: The two-dimensional structure of the camera. (1 pressure ring, 2 lens barrel 3 first lens, 4 second lens, 5 third lens, 6 forth lens, 7 fifth lens, 8 sixth lens, 9 spacer, 10 flange).  
Figure 5: Schematic diagram of the design of the outer baffle.  
When designing the vanes, the interval between adjacent vanes must be accurately calculated. The designed vanes will not block the imaging light in the field of view of the system, so that the vanes can effectively reduce stray light. As shown in Figure 6, first connect point A and edge point C of the baffle with the wall thickness at E0, which is the first vane; connect point \(D\) at the edge with the first vane's edge point E0. Intersect the outer baffle at point E1, connect point A and point E1 at the edge of the baffle and the wall thickness at point E2 to determine the next vanes, and design the vanes in this way.  
Calculate the position and height of the vanes in the two-dimensional drawing software, and the number \(n\) of the vanes and the interval '1' between each vanes satisfy the Equation (6):  
\[(n-1)l=L \tag{6}\]  
The length of the camera baffle \(L\) = 61 mm according to the design index requirements to set 4-level vanes; from Equations (5) and (6), \(l\) = 20 mm; set the thickness of the vanes to 0.25 mm.