# New Optical Design Method of Floating Type Collimator for Microscopic Camera Inspection
## 4 Conclusions  
The collimator optical system has been widely used to reduce the space required for measuring the resolution of mobile phone cameras. Recently released mobile phone cameras have shorter shooting distances. This means that objects can be shot at a close range. When the object distance that the camera can take is extremely short and only one lens group is moved, the optical system aberrations become quite large. To solve this problem, two or more lens groups must be moved to sufficiently correct aberrations in the shortest close range. Therefore, the optical system must be configured as a floating type.  
The collimator used to measure the resolution of the mobile phone camera must also be designed to change the virtual image distance to the target. For this, some of the lenses that make up the collimator must move. In addition, the field angle of mobile phone cameras has gradually widened. It is therefore necessary to minimize the resolution change of the collimator according to the lens group movement. Thus, in this study, a collimator was designed as a floating type that moves two lens groups. Our designed collimator can change the virtual image distance from infinity to 200 mm. Because the MTF of the collimator did not change significantly according to the virtual image distance, it was possible to measure the resolution at the desired inspection distance of the mobile phone camera. Distortion varies from +9.33% to +13.94%, which is a large value compared to that of general optical systems. This is because the designed collimator is about to stop, and the structure is asymmetric. Considering the distortion of the collimator, the diagonal size of the target should be 174 mm. Then, the amount of movement of each lens group required to fabricate the optical system was calculated. Therefore, our proposed collimator optical system is designed as a floating type to inspect the mobile phone camera resolution from infinity to close ranges.  
Figure 6: Locus (**left**) and magnification (**right**) for our designed final collimator system.  
**Author Contributions:** Conceptualization, S.C., J.R. and H.C.; methodology, S.C., J.R. and H.C.; writing--original draft preparation, S.C., J.R. and H.C. All authors have read and approved of the published version of the manuscript.  
**Funding:** This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1A2C4001606). This research was also supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2020R1I1A3052712) and the MSIT (Ministry of Science and ICT), Korea, under the Grand Information Technology Research Center support program (IITP-2021-2020-0-01612) and supervised by the IITP (Institute for Information & communications Technology Planning & Evaluation). This work (Grants No. S2563336) was supported by Business for Cooperative R&D between Industry, Academy, and Research Institute funded Korea Small and Medium Business Administration in 2019.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are included within the article.  
**Conflicts of Interest:** The authors declare no conflict of interest.