Least-squares calibration method for double-grating interferometers used in measurement of long-focal-length lenses.

Abstract

In this paper, we propose a new calibration method for long-focal-length measurement using a double-grating interferometer. A numerical analysis of the relative error in measurement proves that the main factor affecting accuracy is the angle of inclination between grating grids. Hence, we present a least-squares calibration method using a series of lenses to correct this error. Experiments conducted to demonstrate high precision in wide-range focal length measurement (5-85 m) exhibited an error lower than 0.1% and a repeatability better than 0.03%.