Abstract
The paper describes an automatic recording microdensitometer based on the Dobson splitbeam type of instrument, using a single lamp and single photocell. The shutter is driven at a non-synchronous speed and an electromechanical transducer is used to convert the output to a synchronous frequency. This output is used to operate a servomechanism which moves a straight photographic wedge and also a potentiometer. The output from the potentiometer drives a standard pen recorder. The fim carriage has movements of 28.5 cm and 12.5 cm in perpendicular directions and accurate measurements of these displacements can be read on scales permanently in place.

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