Tent and Camera : The Tools of Bird-Photography. 



33 



Series ii a, 6 inch, speed ; Convertible Anastigmat, Series vii a, combined equivalent 

 focus 8 inches, speed 6 f ^ ; Extra Rapid Universal Lens, Series D, 9 \ inch, speed {.' 



The convertible anastigmats are convertible in two or three lenses of different 

 foci, according as the single anastigmats are of equal or different focus. They thus com- 

 bine in a single lens the possibilities of working with short and long focus, the greatest 

 speed being obtained when each system of the doublet has the same focus. 



Fig. 25. Female Brown Thrush stepping into her nest to brood. 



In photographing animals close at hand the anastigmatic qualities of a lens count for 

 little. It is depth of focus combined with high speed which are most needed, conse- 

 quently any lens possessing these qualities will answer. 



One of the most difficult problems in bird-photography has hitherto been that of ap- 

 proach within " shooting " distance. The control of the nesting site, and the use of the tent 

 offer a solution so far as life at the nest is concerned, in at least many species, and the 

 tent in its general use does away with the need of the very long focus or telephoto 

 lenses. 



1 These lenses are made by the Bausch & Lomb Optical Co., Rochester, N. Y. 



