Abstract
In this paper, we consider how much coherence is admissible without affecting the linearity of a microdensitometer. Conditions required for linear operation are presented and discussed. We investigate the strength of these conditions by using differences between the shape of high-contrast- and low-contrast-edge images. The normalized image irradiance is calculated, based upon the theory of partially coherent image formation assuming diffraction-limited optics. Our results show that the numerical aperture of the influx optics must be greater than the numerical aperture of the efflux optics. Higher detail content of the sample requires increased overfilling of the efflux optics. In addition, the coherence interval at the source aperture (or preslit) must be equal to or less than the resolution limit of the microdensitometer when both distances are referred to the scale of the sample plane. Greater incoherence is required as the sample-detail content increases. These results are equally applicable to color or conventional microdensitometry.
© 1972 Optical Society of America
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