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SIDLE AND POALK'S SUBSTAGE IRIS DIAPHRAGM
c. 1880
The iris attachment, which at first seems to resemble an objective, was invented by Sidle & Poalk.
It was reported in the JRMS on page 1053 of volume III part 2, 1880, and also in the English Mechanic and World of Science in 1881. In the latter publication, the fitting into Sidle & Poalks inexpensive centerable substage fitting was noted.
The diameter of the opening is controlled by rotating the upper knurled ring.
