Cameras, Lenses, and Shutters 47 



utes, and is also capable of being left open in 

 order to give an exposure of any length of time 

 that is required. As I have said elsewhere, the 

 time marks on a shutter should never be abso- 

 lutely relied upon, as they are put there more to 

 aid us in judging the differences rather than the 

 absolute measurements of time. 



The focal plane shutter is one that, as its name 

 implies, works on a plane. It is composed of a 

 black curtain that crosses in front of the plate. 

 This curtain is divided in the centre by a slit that 

 can be made wider or narrower at the will of the 

 operator, and as this slit is the entire width of 

 the plate and exposes in its passage only one sec- 

 tion of the plate at a time, we are enabled by the 

 use of this shutter to get the greatest amount of 

 illumination in the shortest space of time. This 

 shutter is capable of being worked automatically 

 and with almost absolute exactness, giving ex- 

 posures ranging from about -^ to xoVo °f a sec " 

 ond. Obviously, for very rapid work it is the 

 only one that can be used. 



No matter what style of shutter we are using, 

 we should learn to know it and its capabilities 

 thoroughly, and be able to judge quickly and 

 accurately how to set it for any given exposure, 

 so that as little time may be lost in manipula- 

 tion of the shutter as possible, for in nature 

 work time is very valuable, and the quicker we 



