Mr. XuYang Li Profile

XuYang Li

at Northwestern Institute of Nuclear Technology

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Proceedings Article | 5 November 2020 Paper

Research on focal length measurement of telephoto lens based on Polaris observation

Xin Zhou, DeChao Liu, ZhiXiang Zhang, Rui Cao, XuYang Li, XiangLong Gu

Proceedings Volume 11570, 115700K (2020) https://doi.org/10.1117/12.2579825

KEYWORDS: Collimators, Computer programming, Cameras, CMOS cameras, Moire patterns, Imaging systems, Spectrum analysis, Optoelectronics, Optical testing

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This paper proposes a improved method for measuring the focal length of a telephoto lens. In this paper, a photoelectric theodolite with high accuracy of angle measurement is used. Besides, a CMOS camera is used to take a position image of the center point of the theodolite, and the corresponding azimuth displayed by the theodolite is recorded. Leveling the optoelectronic theodolite on the open field, Polaris is used as a point light source outdoors. Adjusting the point target on the CMOS image, by which the target is placed in the view center of the field (crosshair center). And then, the pitch and azimuth data of the device are recorded. Adding disturbance to the photoelectric theodolite, the CMOS images is recorded. Adapting methods of target feature segmentation, sub-pixel positioning is performed on the point target image which captured by the CMOS camera. And the point target coordinates is obtained. Finally, the result based on the theodolite angle offset, sub-pixel offset and elevation angle data is calculated. The perturbation data is averaged to calculate the focal length of the telephoto lens. Compared with equipment testing result of focal length, experiments have achieved high measurement accuracy. And this method is suitable for detecting the focal length of an optoelectronic device in an outdoor environment.

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