THE BIRD PHOTOGRAPHER’S OUTFIT 11 
using two lenses, the great size and weight of a 
long-focus lens are drawbacks. These objections are 
largely overcome by the use of the symmetrical 
lenses placed in most of the long-focus boxes, or, if 
expense be not considered, by a “convertible” lens. 
For several years I have used a “ Victor” lens, 
sold with the “Premo” long-focus camera. The 
combined focus of the front and back lenses is seven 
and a half inches, of either of the lenses alone, fif- 
teen inches. The single lens therefore, the distance 
being the same, gives an image double the size of 
that cast by the two lenses together. 
This lens has been thoroughly tested, and many 
of the pictures given in this book were made with it. 
When the conditions are favorable and the subject 
not extremely difficult it yields satisfactory results. 
The “convertible” lenses of various makers are 
also separable, and where the rear and front lenses 
are of different foci three focal lengths are obtain- 
able. These lenses are of the highest grade, and 
consequently expensive. In a bright light, or where 
great speed is not required, they do not seem to be 
as superior to the trade lens as the much higher 
price would lead one to expect. But in dull days, or 
in the shadow, or where extremely rapid exposures 
are necessary, their superior qualities become evi- 
dent. My experience with these convertible lenses 
has been limited to the Zeiss Anastigmat, Series 
VII a, of which I am now using a No. 10 with a 
combined focus of eight-inches, the front and rear 
lenses both having a focal length of fourteen inches. 
This combination is preferred to one in which the 
component lenses are of different foci, because of the 
