Abstract

A theory is presented to account for the fact that a photoconductive cell can detect when an image projected on it is in sharpest focus. Each of the small particles in the photoconductive surface is treated as an individual photoconductor in series–parallel connection with all the other particles. When the distribution of light on the surface of such a photoconductive cell is varied (total incident flux being constant) the total conductance across the whole surface of the cell depends upon detail contrast, acutance, and other factors of the projected image. The observed dependence of conductance on sharpness of focus can be explained by this theory.

© 1964 Optical Society of America

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References

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  1. D. R. Craig, Phot. Sci. Eng. 5, 337 (1961).
  2. C. P. Hadley and S. E. Fisher, RCA Rev. 20, 640 (1959).

1961 (1)

D. R. Craig, Phot. Sci. Eng. 5, 337 (1961).

1959 (1)

C. P. Hadley and S. E. Fisher, RCA Rev. 20, 640 (1959).

Craig, D. R.

D. R. Craig, Phot. Sci. Eng. 5, 337 (1961).

Fisher, S. E.

C. P. Hadley and S. E. Fisher, RCA Rev. 20, 640 (1959).

Hadley, C. P.

C. P. Hadley and S. E. Fisher, RCA Rev. 20, 640 (1959).

Phot. Sci. Eng. (1)

D. R. Craig, Phot. Sci. Eng. 5, 337 (1961).

RCA Rev. (1)

C. P. Hadley and S. E. Fisher, RCA Rev. 20, 640 (1959).

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Figures (5)

Fig. 1
Fig. 1

1/d2 falloff curve and focus detecting curve.

Fig. 2
Fig. 2

The conductor matrix. Conductors g11, g21, gaa, etc., represent individual particles of the photoconductive layer.

Fig. 3
Fig. 3

Effects of rotating a sharply focused line target relative to the electrodes. For γ=1, rotation from 0° to 90° is represented by typical Curves A through E. For γ<1, rotation from 0° to 90° is represented by typical Curves A through D. For γ>1 rotation from 0° to 90° is represented by typical Curves B through F. Note that the amplitude changes, but not the distance over which the change occurs.

Fig. 4
Fig. 4

The effect of dot % in a target. Curve A is from a print of a halftone screen, i.e., low acutance. Curve B from a print of a tint screen, i.e., high acutance. Compare with Curve C, printed on high contrast emulsion from a Ronchi ruling. Here the peak sensitivity occurs at 50%.

Fig. 5
Fig. 5

Effects of target frequency. Broad hump (A) for low-frequency target, indeterminate output (B) for too low a target frequency, and well-defined position, but low in amplitude (C) for maximum target frequency.

Equations (10)

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G a = g 0 ( m / n ) L n γ ,
G b = g 0 ( m / n ) 1 2 ( L 1 γ + L 2 γ ) ,
G c = g 0 ( m / n ) [ 2 L 1 γ L 2 γ / ( L 1 γ + L 2 γ ) ] ,
g s = g 0 L 2 - L 1 n log ( L 2 / L 1 ) .
g i = 2 g 0 L 1 L 2 / n ( L 1 + L 2 ) .
g 0 ( L 2 - L 1 ) n log ( L 2 / L 1 ) > 2 g 0 L 1 L 2 n ( L 1 + L 2 ) .
L 2 - L 1 log ( L 2 / L 1 ) > 2 L 1 L 2 L 1 + L 2 .
( A - 1 ) L 1 log A > 2 A L 1 2 ( A + 1 ) L 1
A - 1 log A > 2 A A + 1 .
( A - 1 ) ( A + 1 ) 2 A > log A ,