The Microscope. Its History, Construction, and Application 15th ed. / Being a familiar introduction to the use of the instrument, and the study of microscopical science

by Jabez Hogg

THE DIAPHRAGM.

Fig. 150.—The Diaphragm.

The early form of diaphragm in use was that shown in [Fig. 150].

Fig. 151.—Shutter Diaphragm.

It consists simply of a circular brass plate with a series of circular openings of different sizes, arranged to revolve upon another plate by a central pin or axis, the last being also provided with an opening as large as the largest in the diaphragm-plate, and corresponding in situation to the axis of the microscope body. The holes in the diaphragm-plate are centred and retained in place by a bent spring in the second plate, which rubs against the edge of the diaphragm-plate and catches in a notch. The blank space shuts off the light from the mirror when condensed light is about to be used. It is usually made to fit in under the stage of the microscope. This has been almost superseded by the iris diaphragm, originally designed by Wales, of America. It was made by this optician for his working students’ microscope. An early form of the iris diaphragm is seen in [Fig. 151]. By pressing upon the lever handle at the side the aperture gradually closes up, and without for a moment losing sight of the object under examination.