The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Shutters, Instantaneous
working behind the lens, (c) those working in the diaphragm slot, {d) those working in frgnt of the sensitive plate.
(a) Shutters Working in Front of the Lens. The object of the somewhat elaborate way in which this subject is treated in the following notes is to provide a practical guide to the choice of a shutter. We may again divide into classes -
(Class II., a i) The Simple Drop. This consists of a sliding piece of wood or ebonite, with an aperture which, passing in front of the lens, makes the ex-posure. The longer the aperture in the dropping piece the more even the illumination of the plate. From theoretical considerations the aperture should take the form shown in the accompanying dia-gram (fig. 114), the distance along the dotted line A B being made equal to, or twice, or thrice, the diameter of the lens: the narrower this aperture the quicker the ex-posure, but the less light admitted during exposure. The longer the slide drops before uncovering the lens, the more even the illumin-ation of the plate and the shorter the exposure. In this, as in all shutters fitting on the hood of the lens, the aperture of the shutter should never be smaller than the lens aperture, or it acts as a stop. Some of tfie drop-shutters are so arranged that the aperture may be elongated or shortened by an additional sliding piece.
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