108 



HANDBOOK OF PHOTOGRAPHY 



been used a great deal. It is reliable so long as it can be kept clean, but this is hardly 

 possible in a hand camera that is exposed to dust when in use. A later method, first 

 made practical in 1910, depends on the braking action of a train of gears or an escape- 

 ment-wheel mechanism of some kind. This gear and escapement retarding device 

 is now considered the most accurate yet devised and is used on all modern interlens 

 shutters. 



With three separate mechanisms built into one small casing, it is not surprising 

 that a photographic shutter is a complicated mechanism. It has to be to fulfill the 

 functions of diaphragm action and timing control. Figure 11 is a drawing of the 

 complete assembly with lenses attached. The mechanical clearances are very small 

 especially in the smaller outfits, and this is one reason why amateur repairs nearly 

 always end up by ruining the shutter completely. The remarkable fact about shutters 

 is that designers have been able to put so much mechanism into a small space and 



that manufacturers have been able to 

 make them perform reliably. 



Automatic Action. — There is one other 

 point to be considered in this short outline; 

 the difference between automatic shutters 

 and those that have to be set for each 

 exposure. Early shutters were all the 

 second type ; there was a setting lever plus 

 a release lever, and two operations were 

 required to complete the exposure. This is 

 a disadvantage that was recognized at the 

 beginning of shutter development. Auto- 

 matic shutters were attempted by designers 

 as early as 1892. The principle had 

 already been demonstrated in the trigger 

 action of automatic revolvers. As applied 

 to shutters, this trigger action consists of some mechanical arrangement of two springs 

 on the main lever of a shutter in such a fashion that the shutter blades are closed by 

 spring 1 after being forced by hand against the pressure of spring 2; i.e., spring 2 

 opens the blades when released after tension is applied to it by hand. After its action 

 of opening the blades, it is disconnected from the lever by a slip catch (or some similar 

 device) and spring 2 is then free to close the blades. 



It is a simple device mechanically, and there are many ways to accomplish this 

 automatic feature of shutter action. But there is, as usual, a disadvantage. In 

 automatic shutters spring 2 must open the blades against the pressure of spring 1, 



Table III. — Wollensak Shutter Dimensions 



4 2 

 Fig. 18. — Retarding device for Wol- 

 lensak Betax shutter. 1, lever engaging 

 pinion on escapement; 2, escapement; 

 3, pallet whose number of oscillations 

 are controlled by escapement 2; 4, pallet 

 lever, offering resistance and providing 

 smoothness of operation; 5, slot in escape- 

 ment balance in which pallet lever rides. 



Number 



Over-all length, in 



Diameter case 



Maximum diaphragm opening 

 Front lens opening 



Threads, per in 



Back lens opening 



Threads, per in - 



Length flange hub, in , 



Diameter flange hub 



Threads, per in 



0.710 

 1.521 

 0.552 

 0.838 



50 

 0.838 



50 

 0.177 

 0.953 



40 



0.808 

 1.970 

 0.710 

 1.059 



50 

 1.059 



50 

 0.197 

 1.185 



40 



0.827 

 2.345 

 1.024 

 1.204 



50 

 1.204 



50 

 0.197 

 1.325 



40 



0.946 

 2.940 

 1.380 

 1.764 



40 

 1.764 



40 

 0.293 

 1.997 



30 



1.024 

 3.705 

 1.761 

 2.389 



40 

 2.389 



40 

 0.316 

 2.623 



30 



1 



4 



2 



2 

 40 



2 

 40 



0.335 



3.128 

 30 



.024 

 .660 

 .233 

 .901 



.901 



