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TitleA focus effect in some thermal imaging systems
Publication TypeConference Paper
Year of Publication2013
AuthorsSaunders, P., and White D.R.
Conference NameAIP Conference Proceedings
Date Published2013
AbstractWe have recently become aware of a focus effect in some thermal imaging systems that can lead to errors in the measured radiance of up to 20%. The cause of the effect is a design flaw in which the aperture stop of the lens moves during focusing, resulting in a change in the solid angular field of view of the system. Unless the focus is set to the same distance as used during the manufacturer's initial calibration, the readings on these instruments in use and during subsequent recalibration will be in error. In most cases, the initial calibration focus setting is unknown to the user, so elimination of the error is a matter of chance. This paper describes a procedure to evaluate the error during recalibration and provide a means for the user to correct readings during use based on the focus setting. © 2013 AIP Publishing LLC.

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