# New Optical Design Method of Floating Type Collimator for Microscopic Camera Inspection
###### Abstract  
Recently released mobile phone cameras are capable of photographing objects at a fairly close distance. In addition, the field angle from the camera has increased. To measure the resolution of a mobile phone camera, the target must be photographed. To measure the resolution according to the object distance change from a mobile phone camera with a wide field angle, the target size must be large, whereas the target position must be moved. However, the target size cannot be changed. A virtual object for the target was created using a collimator. Moving a part of the lens group constituting the collimator also changes the virtual object distance. If the amount of change in the virtual object distance is large, the resolution of the collimator may also change. Therefore, a collimator that maintains the resolution even when the distance of the virtual object changes is designed as a floating type in which two lens groups move. Therefore, we propose a new floating collimator optical system that can inspect the resolution of mobile phone cameras from infinity to a close range to compensate for aberrations caused by object distance changes. ao 2021 28 June 2021 4 (July 2021) 2021 2021 2021 2021 2021 2021 2021 2021 2021 2  
word \"floating\" is a very popular word in camera optics [7]. Optical systems that move two or more groups of lenses to correct the image distance are called \"floating optics\". The optical system proposed in this paper changes the position of the virtual image by moving two or more lens groups. The collimator, which can change the virtual image distance from a real target, is widely used in an optical inspection, such as optical resolution test of optical lens systems or surface inspection of optical instruments [8; 9]. In the performance test of an optical system, the collimator is placed between the target, or test chart in some cases to inspect the lens system, collimating the incident test light to plane light source and changing the focal points [10; 11; 12; 13]. In most cases, the target includes a light source to improve the test. The test light emitted from the sources passes through the transparent target or is reflected from the target and enters the collimator [14]. The test light changes through the collimator to a type that allows the optical lens system to be inspected. A couple of subsidiary lenses may be added to change the image distance of the test lens aligned with the collimator [10; 11; 13]. Although the collimator employed in the lens inspection device can be composed of a single lens, it is composed of multiple lenses to correct the spherical and chromatic aberrations [12; 15]. The collimator is essentially used as a device for making a plane light source to inspect the surface of optical instruments [16; 17; 18; 19]. The light from the test chart passes through the collimator to become a collimated beam, and is introduced into a lens system that has a specific focal distance and is incident on the surface of the optical instrument under inspection. The collimator provides collimated light to the focusing lens, which adjusts the test light to a specific focal distance [16; 18; 20]. The light reflected from the surface of the optical instrument passes through the intermediate lens system, resulting in an image on the test chart. This is the base image used to determine the defects on the optical instrument surface. The collimator consists of multiple lenses, some of which are moving to vary the inspection area [17; 21]. Furthermore, the collimator is employed as a focal distance changing device to focus on various layers in an optical pickup device that reads the data from multi-layered optical  
Figure 1: Layout of inspection instrument of mobile phone camera optics. disks [22; 23]. The collimator makes the light emitting from the light source parallel, and the consecutive lens system creates a focus on the optical disk, whose height changes as a part of the lens system moves.