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Revolving Diaphragm

Revolving Diaphragm

1844
Three aperture optical diaphragm, for Quartz spectrograph (E.31)

Three aperture optical diaphragm, for Quartz spectrograph (E.31)

1932
Special Watkin's Diaphragm designed to give equal spaces between U.S. values for a calculating shutter

Special Watkin's Diaphragm designed to give equal spaces between U.S. values for a calculating shutter

1902