Design Considerations for a Linear Microdensitometer

John P. Fallon

doi:10.1117/12.7971663

1 December 1973 Design Considerations for a Linear Microdensitometer

John P. Fallon

Author Affiliations +

Optical Engineering, Vol. 12, Issue 6, 126206 (December 1973). https://doi.org/10.1117/12.7971663

Abstract

Tradeoff studies and tests on the various subsystems of a microdensitometer have resulted in a recommended design configuration for a Linear Microdensitometer. The photometric subsystem includes laser sources suitable for color operation, an illumination system capable of producing a 1 um spot on the film, a wide angle collection system (NA = 1.0), a photodiode detector, and digital density conversion. Performance of the photometric system was verified by breadboard tests. The results include an MTF (square wave response) of 99 percent at 200 Qp/mm and 90 percent at 500 kp/mm, and linearity (object independence) to greater than 400 Qp/mm. The photometric precision is ±0.01 D from 0 D to 2 D and ±0.02 D from 2 D to 4 D. These specifications are attained at scanning speeds up to 8000 samples per second. A two-beam optical system and automatic focus control ensure photometric repeatability. The two-axis stage is driven by phase-locked loop servos incorporating interferometric position sensors. The servos permit scanning at skew angles, obviating stage rotation. The stage sub-system is precise to within ±0.5 pm over 5 inches of travel. Stage speed is variable from 0.4 mm/sec to 40 mm/sec. Human factors features include rapid sample acquisition by virtue of a viewing system with magnification variable from 16X to 200X and simplified operator control through a CRT graphic terminal.

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John P. Fallon "Design Considerations for a Linear Microdensitometer," Optical Engineering 12(6), 126206 (1 December 1973). https://doi.org/10.1117/12.7971663

Published: 1 December 1973

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