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Open AccessArticle

A Novel Focal Length Measurement Method for Center-Obstructed Omni-Directional Reflective Optical Systems

1
Department of Medical IT Convergence Engineering, Kumoh National Institute of Technology, Gumi-si 39253, Korea
2
Department of Optical Engineering, Kumoh National Institute of Technology, Gumi-si 39253, Korea
*
Author to whom correspondence should be addressed.
Appl. Sci. 2019, 9(11), 2350; https://doi.org/10.3390/app9112350
Received: 22 May 2019 / Revised: 3 June 2019 / Accepted: 5 June 2019 / Published: 8 June 2019
(This article belongs to the Special Issue Advanced Ultrafast Imaging)
An omni-directional optical system can be used as a surveillance camera owing to its wide field angle. In cases in which a system is designed with a central screen obscuring structure to increase the resolution of the off-axis field, however, the conventional methods cannot be used to measure the effective focal length (EFL). We assumed the actual and theoretical distortion values of the fabricated optical system to be the same and determined the system’s EFL by finding the minimum deviation point of the measured and theoretical distortions. The feasibility of the determined EFL was verified through a tolerance analysis of the system. For these precise measurements we also analyzed the sources of error. To verify our proposed measurement method, we measured the focal length of a center-obstructed omni-directional reflective optical system with an 80–135° field of view (FOV). The EFL from the measurement was 0.3739 mm and was only approximately 11 µm different from the EFL calculated using the design software. Thus, the reliability of focal length measurements in omni-directional optical systems was improved. View Full-Text
Keywords: omni-directional reflective optical system; focal length measurement; geometrical optics; optical design; tolerance analysis omni-directional reflective optical system; focal length measurement; geometrical optics; optical design; tolerance analysis
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MDPI and ACS Style

Choi, H.; Jo, J.-Y.; Ryu, J.-M. A Novel Focal Length Measurement Method for Center-Obstructed Omni-Directional Reflective Optical Systems. Appl. Sci. 2019, 9, 2350.

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