The Dictionary Of Photography

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

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Shutters, Instantaneous
Iris Diaphragm Action. Several new shutters have lately been introduced of this pattern.
(CI. II., c 7) Rotating Screen. In this form a screen pierced with a circular aperture rotates across between the lenses.
-(CI. II., d) Shutters Working in front of the Sensitive Surface. - In this form of shutter, which is by no means new, a roller blind with a narrow slit in it, passes immediately in front of the sensitive surface, thus ex-posing the same in successive portions,- and allowing the lens to act with full aperture for the whole period of exposure - nq matter how short that exposure be. This shutter also possesses the advantage of allowing any focus lens, or a lens of any diameter, being used without any difficulty.
As to make a choice of shutters it is necessary to understand something of the manner in which they act, we will first of all show the lens working at full aperture fig. 115. From this it will be seen that far more light is transmitted axially, that is, with the horizon rays, than with the sky and foreground, but if the lens is stopped down toas shown
in fig. ■the illumination is prac-tically equal. For this particular portion of my notes shutters are only divided into four main classes : - -a, those acting in front
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