12 BIRD STUDIES WITH A CAMERA 
greater speed of the two when combined, and fur- 
thermore, because, being of the same focus, they 
could, if occasion arose, be used in a twin-lens box. 
The speed of the combination is registered at F. 6.3; 
that of the single lenses at 12.5. With the former 
the most rapid exposures can be made successfully, 
while the latter are sufficiently fast to permit of 
ordinary instantaneous work. This lens is stated 
to cover a 5 X 84 plate, and when in use on a 4X 5 
camera gives a high degree of illumination and per- 
fect definition. 
The telephoto lens may be employed in certain 
kinds of bird photography with not unsatisfactory 
results. Its disadvantages are lack of speed, an ex- 
posure of at least one half a second to a second being 
required at F. 8 in bright sunlight, the necessity 
of extreme care in focusing, and of absolute rigidity 
of the camera at the time of making the exposure. 
In short, the telephotographer needs more time, 
both before and after pressing his bulb, than the 
bird photographer is often accorded. However, with 
such subjects as nests high in trees or on cliffs, 
Herons and other shore-inhabiting birds, Ducks on 
the water or Hawks perched in leafless trees, the 
telephoto will be found serviceable. 
Negatives are frequently secured in which the 
figure of the bird, while small, is sharp, when, by 
enlargement, a desirable picture can be made of 
what in the original was too small to be easily dis- 
tinguishable. An increase in size of two diameters 
is possible from any fairly sharp negative, but if the 
object be in perfect focus an increase of four diame- 
ters may be made. 
