Encyclopedia of Biometrics

2009 Edition
| Editors: Stan Z. Li, Anil Jain

Focal Length

Reference work entry
DOI: https://doi.org/10.1007/978-0-387-73003-5_517

With respect to a lens or mirror, the distance from the lens or mirror at which a parallel beam of light rays will be focused to the smallest size possible for the lens or mirror. The focal length of a simple converging (convex) lens can be measured by focusing the rays from the sun to the smallest point possible and measuring the distance from the image to the lens.

 Face Device

 Iris Device

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