The precision optical lens and optical focus design make optical diameter of the temperature testers within **0mm away as *3mm, and then the optical spot sizes will become greater with the change in the distance, e.g. the optical spot diameter at 1.2m away is *0mm. ratio of the temperature tester to the size of the optical size is also called optical resolution. The optical resolution of CT-S is *5:1, and the corresponding optical spot sizes can be calculated by the ratio as *5:1 of the distance to optical spot size.