SHUTTERS 



109 



therefore it must be stronger than spring 1. From this it follows that an automatic 

 shutter never closes so fast as it could if it did not have this double-spring feature. 

 For this reason the fastest interlens shutters are not the automatics but are of the 

 type that must be set by hand before each exposure. 



Table IV. — Dimensions — Wollensak Studio Shutters 



Focal -plane Shutters. — Interlens shutters have certain disadvantages: (1) maxi- 

 mum speed at present is about V^oo sec; (2) their efficiency at high speeds is low; (3) 

 shutters of large size are always slower than small ones of the same design on account 

 of the increased friction and the inertia of the parts that must be set in motion. This 

 is a decided disadvantage with large-aperture lenses and has led to an almost universal 

 use of focal-plane outfits for high-speed photography. 



Fig. 19. — ^Curtain of Graflex shutter. 



R.B.GRAFLEX- SERIES D 



CURTAIN APERTURE 





The focal-plane shutter is simply a black curtain, like a window shade, on two 

 rollers with slits of different width cut across it. Figure 19 is the curtain which can 

 be wound to use any one of four slits. (The square opening at the top is for time and 

 bulb exposures.) The spring tension on the curtain is also variable and is controlled 

 by a separate winding key. The results, expressed in reciprocals of 1 sec, are tabu- 

 lated on the index plate, Fig. 20. The whole 

 outfit, fitted in its frame and assembled on 

 the back of a Graflex camera, is illustrated 

 and described in Fig. 21. This is probably 

 the simplest form of focal-plane shutter. 



In the Leica camera the design has been 

 changed to provide a slit of variable width 

 instead of a number of slits, and the film- 

 winding mechanism has been geared to the 

 shutter-winding shaft so that both oper- 

 ations are performed with one motion. 

 This shutter is now actually made up of 

 two curtains. The separation of the ends 

 is the slit of variable width. Slit width is adjusted to the proper value, in setting the 

 shutter for exposure, by winding up the curtains on one roller. When released, spring 

 pressure on two separate rollers at the other end of the camera draws the two curtains 

 across the film aperture as a unit. The range of rated speeds on the latest Leica 

 cameras is from 1 to ^ooo sec 



440 , 135 50 _ 



I 55.0 I60 " 65 



680 195, _75 



I 82 5 235 ' 80 



I lOOO I Z95 1 90 I . 



THE FOLMER GRAFLEX 



CORPORATION 

 .. ROCHESTER. N. Y., U.S.A. 



Fig. 20. — Index plate for setting 

 speed of Graflex shutter. 



the 



