## 3 Methods  
### Primary Design Approximation of Optical Lens  
The design software used in this study was CODE V (Synopsis, Optical system design Inc., East Boothbay, ME, USA). Figure 2 illustrates the optical path for the optical system of Example 1 from the patent JP20160012034A2P. In Figure 2, beginning at the object side to the sixth surface, the object serves as a converter to rapidly change the angle of view, and the sixth surface to the twenty-seventh surface forms shape of a double-gauss type for the incoming rays. This optical system has optical specifications of F/# 1.4 and EFL of 24 mm, and the applied imaging sensor size satisfies 21.7 mm of full-frame. However, the AF system is a floating type optical system focusing on the third group from the 12 th surface of the optical system to the 16 th surface and the fourth and fifth groups from the 18 th surface to the 27 th surface. As it has a flange back distance for DSLR, it does not match the flange back distance for the CSC design. Figure 3 shows the optical path for the optical system of Example 1 from the patent KR1020140124286 AP. The first to sixth surfaces on the object side act as converters, and the seventh surface to the 21 st surface serve as the imaging unit, and the focusing is performed with the single lens of the 13 th surface. This optical system has the flange back distance for the CSC optical system capable of AF with internal focusing using a single F/# of 1.4, and the imaging sensor has a full-frame size of 21.7 mm or APS-C size of 14.25 mm is not satisfied. Therefore, by combining the two optical systems appropriately, basic design data that satisfies both the F/# of 1.4, AF with the internal focusing method using a single lens and a full-frame imaging sensor was obtained. The 1 st surface to The 11 th surface of the Example No. 1 optical system from the patent JP 20160012034A2P (Figure 2) and the 7 th surface to The 21 th surface of the Example No. 1 optical system from the patent No. KR1020140124286 AP (Figure 3) were synthesized. Prior to combining the two optical systems, the KR1020140124286 AP optical system was adapted to meet the specifications of the APS-C sensor such that it was extended to the size of a full-frame sensor. Each focal length of the synthesized lenses was compared with the optical systems of JP20160012034A2P and KR1020140124286 AP, and the group with minimum variance was then selected. For example, the focal distance from the 12 th surface to the 27 th surface of the JP20160012034A2P optical system is 43.508 mm, and the focal length from the 7 th surface to the 21 st surface of the KR1020140124286 AP optical system is 45.926 mm, which is a relatively small focal length difference from other lens groups. The objective of the synthesis of the two optical systems is to replace the imaging group of the JP20160012034A2P optical system with the imaging group of the KR1020140124286 AP optical system in such a way that the paraxial optical properties of the optical system after synthesis would not differ greatly from the paraxial optical properties of the JP20160012034A2P optical system before synthesis. Therefore, the optical system of JP20160012034A2P is considered as an optical system having a first group from the 1 st surface to the 11 th surface and a second group from the 12 th surface to the 27 th surface. The principal points of each group are determined and the principal point of the optical system is \(-\)98.353 mm from the 11 th surface. Additionally, the first principal point of the second group is 39.255 mm from the 12 th surface of the optical system, the optical distance difference between the two groups is 142.852 mm from the second principal point of the first group to the first principal point of the second group. Likewise, in the KR1020140124286 AP optical system, if the 1 st to 6 th surfaces are referred to as the 1 st group and the 7 th surface to the 21 st surface as the second group.