## 3 Methods
### Primary Design Approximation of Optical Lens
The first principal point of the second group in the KR1020140124286 AP optical system is separated by 27.772 mm from the 7 th surface. As the second group of the JP20160012034A2P optical system is replaced by the second group of the KR2020140124286 AP optical system, the distance from the second principal point of the first group of JP20160012034A2P to the first principal point of the second group of KR1020140124286 AP was supposed to be identical at 142.852 mm. Therefore, the distance between the lenses on the 11 th surface  
Figure 2: Optical layout for JP20160012034A2P, Example 1.  
and the 12 th surface after synthesis should be increased by 16.715 mm, which is the distance between the first principal point of the second group of JP20160012034A2P and the first principal point of the 2 nd group of KR1020140124286 AP. Specifications of the optical system as shown in Figure 4 are shown in Table 1.  
The optical path of the synthesized optical system is shown in Figure 4. The EFL of the synthesized optical system is 26.302 mm, which is the difference between the designed target of 24 mm and 2.3 mm at 5 degrees field of view. In addition, the BFL is 10.83 mm, which is shorter than the standard CSC flange back specification. Considering that this optical design is a very wide angle system intended for the CSC format, proper correction of the focal length and back focal length is essential and so this was adjusted by solving the simultaneous equations of Equation (2). Here, the lens surface selected to correct each day's radiation must be capable of physical fabrication, where the curvature and thickness after correction must not be largely changed from the existing values. Additionally, as there is no real numeric solution in the quadratic equation to find the solution of the focal distance, various combinations of variables were applied, and then, R1, R4, and D11 variables were selected. R1 is the curvature of the first surface, R4 is the curvature of the fourth surface, and D11 is the lens thickness of the 11 th surface. When the variables R1, R4, and D11 were selected and the BFL was corrected to 15 mm, the changed values of each variable were as illustrated in Table 2. At this point, if a second correction is performed to adjust the focal length to 24, it was confirmed that the parameters of R2, R3, and R25 variables changed as illustrated in Table 3. In this case, variable selection was chosen by examining the variable combinations as mentioned above. \begin{table}
\begin{tabular}{c c} \hline \hline EFL & 26.302 mm \\ BFL & 10.830 mm \\ FFL & 19.457 mm \\ F/\# & 1.4 \\ Image distance & 10.830 mm \\ Overall length & 122.481 mm \\ Paraxial image height & 21.7 mm \\ HFOV (Half Field of View) & 39.5\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: First orders of optical layout after combining the optical layout of JP20160012034A2P and the optical layout of KR1020140124286 AP. Figure 3: Optical layout for KR20140124286 AP, Example 1. Figure 5 illustrates the optical path when the BFL of the synthesized optical system is adjusted and the EFL is corrected to 24 mm. It is evident that the light aberration is very large through the optical path of Figure 5. In the optical design software, design optimization is the process to minimize the size of the surface area. Allowing large aberrations in the central part of the basic design process can be detrimental in the early stages of the optimization process, especially as the center size is more sensitive to the surface size. Hence, design optimization should proceed after correcting the aberration to some extent. To that end, the aspherical contribution to the Seidel 3 rd order aberration was used [17]. As the aim of the aberration correction in the basic design process is to further smoothen the design optimization at the initial stage, spherical aberration, the factor with a considerable effect on gathering the ray to one point with respect to the central part of the upper surface, was corrected.