20 BUM) STUDIES WITH A C'AMEIIA 



less wlien used for slow exposures of two or tliree 

 seconds, a matter of niucli importance in making 

 time pictures of sitting hirds, who are apt to turn 

 their head if they hear the click of the shutter. This 

 shutter, however, does not respond quickly in slow 

 exposures and is very heavy, a disadvantage in tele- 

 photography. 



The " Unicum " shutter is lighter, responds quick- 

 ly, has a lever to which a tliread may be attached 

 for making exposures from a distance, can be easily 

 diaphragmcd from the rear, but is n<jt wholly noise- 

 less. There are also other shutters, each possessing 

 good ])oints of its own, and the selection of any one of 

 them for use in medium rapid, slow, or time work 

 can be left to the photographer, who should, how- 

 ever, remember that the time scales on these shutters 

 represent degrees of difference and not exact meas- 

 urements of time, and that there is great variation 

 in tlie exposures of different shutters of the same 

 make when sin^ilarly adjusted. Tlius the " cnie fifth 

 of a S('Cf)nd'" of one shutter may be equivalent to 

 the " one second " of another. The scale on most of 

 these shutters calls for a si^eed not exceeding a j^hj- 

 I)art of a second, but this is far too slow an exposure 

 to successfidly ]ihotograpli a ii\-iug bird at short 

 ra,nge when^ a s])eed of at least -jff,, of a second is 

 required. 



For very rapid woi'k the choice is limited to one 

 kind of shutter — that is, the focal-])lane, which in 

 effect is a curtain with an adjustalihi slit wliicli is 

 ])l!iced directly in front of tln^ jtlate. Great speed 

 with this shutti^r is in ■|)a,rt secured l)y increasing 

 the tension of the si)ring, which acts as ils motive 



