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FUNNEL STOP FOR DARK GROUND WORK

YEAR: c. 1935

A cone shaped device limiting the internal aperture of a dark field objective. In use, the device is dropped into the rear opening of the optical part of the objective to provide a reduction of the field of view to eliminate stray light from interfering with the dark background. This device is not needed in objectives which have a built-in iris diaphragm. In the example shown below, the chrome part is unscrewed from the brass part and the funnel stop is dropped into it, so that it restricts the aperture at the top of the optical elements. In this example all the optical elements are housed in the lower chrome portion of the objective, so the stop must be placed in that part in order to reach the rear or top end of those elements.

funnelstop