Focal length measuring device

Details Focal length measuring device Focal length measuring device

2006-09-12

2006-09-12

Toatley, Jr., Gregory J. (Department: 2877)

Optics: measuring and testing

Lens or reflective image former testing

Focal length measuring

Reexamination Certificate

active

07106428

ABSTRACT:
A focal length measuring device comprises a light source unit for generating a collimated light, a diffraction grating for deflecting the collimated light by a deflection angle θ, and an image-pickup element for measuring a position of a focused spot light after the deflected light passes the lens to be tested. The diffracting grating is disposed near a front focal plane of the lens to be tested. The image-pickup element is disposed near a rear focal plane of the lens to be tested. A focal length is calculated according to a relationship such as h=f tan θ under condition that h indicates an image height as a distance from the optical axis. By doing this, it is possible to measure the focal length accurately and easily while restricting an influence of a depth of focus and an aberration.

REFERENCES:
patent: 3870415 (1975-03-01), Cornsweet
patent: 3912395 (1975-10-01), Voggenthaler
patent: 4139305 (1979-02-01), Lapornik
patent: 4832486 (1989-05-01), Gershon et al.
patent: 7-055638 (1995-03-01), None

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