Modulation Measurement Applied to the Focusing of Aerial Cameras

G. C. Brock; P. A. Harrison; N. Smith

doi:10.1117/12.7971593

1 February 1972 Modulation Measurement Applied to the Focusing of Aerial Cameras

G. C. Brock, P. A. Harrison, N. Smith

Author Affiliations +

Optical Engineering, Vol. 11, Issue 1, 110113 (February 1972). https://doi.org/10.1117/12.7971593

Abstract

Photoelectric measurement of aerial image modulation at a single spatial frequency has been applied to the focusing of lenses in aerial cameras. Using an automated apparatus to provide a plot of modulation through focus, the settings are made in a fraction of the time and with much greater confidence than by the photographic resolving power method. It is pointed out that the focus for a single well-chosen frequency can be a good index of the focus for all frequencies in the photographically-important region of the MTF of the lens, also that a through-focus plot of modulation at one or two important frequencies is often of greater value to the camera manufacturer than the usual MTF plot at one focus position. The well-known difficulty in focusing some lenses by high contrast resolving power is explained in terms of their decreased sensitivity to focus setting above a certain frequency; in some cases this effect cannot be eliminated by moderate stopping down. Although primarily designed for measuring relative modulation on axis, the apparatus can be calibrated to read absolute modulation to a useful degree of accuracy, can be used off-axis, and has many photo-optical applications.

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G. C. Brock, P. A. Harrison, and N. Smith "Modulation Measurement Applied to the Focusing of Aerial Cameras," Optical Engineering 11(1), 110113 (1 February 1972). https://doi.org/10.1117/12.7971593

Published: 1 February 1972

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