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Optical Engineering

Design Considerations for a Linear Microdensitometer
Author(s): John P. Fallon
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Paper 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.

Paper Details

Date Published: 1 December 1973
PDF: 7 pages
Opt. Eng. 12(6) 126206 doi: 10.1117/12.7971663
Published in: Optical Engineering Volume 12, Issue 6
Show Author Affiliations
John P. Fallon, Technical Operations, Inc., (United States)

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