4. Lens Test No. 2. Same subject, distance, plate, and date as Test No. 1. Front lens (fourteen-inch focus) of Zeiss Convertible, No. 10; diaphragm F. 16; ¹⁄₂₅ second.
5. The bird in Test No. 2 enlarged about three diameters.
The telephoto gives an enlargement of about six diameters of the image thrown by eight-inch lens, and three diameters increase of that of the fourteen-inch lens. It practically restricts the picture to the immediate surroundings of the bird, and is without focal depth.
6. Lens Test No. 3. Same subject, distance, plate, and date as Tests Nos. 2 and 3. Eight-inch Zeiss Convertible, Series VII a, No. 10, with telephoto attachment; diaphragm F. 8; twenty-one-inch bellows; one second (½ second was later found to be full time).
Having now made three good negatives in the field, we may, by enlargement, improve on the image of the bird obtained. The possibilities in this direction are clearly shown by the three enlargements accompanying the contact prints from their respective negatives. In each instance the enlargement is about three diameters, and the telephoto negative of course furnishes the most satisfactory picture. When the difficulties of telephotography are considered, however, and the ¹⁄₂₅-second exposure of the fourteen-inch lens, which permits of hand work, is compared with the one second of the telephoto, we believe that for general work in photographing birds a lens having a focal length of at least fourteen inches will be found the most satisfactory. It should be added that, in order to make them wholly comparable, the three contact prints as well as the enlargements were made on enameled bromide paper.
7. The bird in Test No. 3 enlarged about three diameters.
The Shutter.—For fairly rapid, slow, and time exposures, a lens shutter, such as is sold with trade cameras, will be found suitable. Simplicity and noiselessness are the chief requirements in this kind of a shutter. The “Iris Diaphragm” shutter is noiseless when used for slow exposures of two or three seconds, a matter of much importance in making time pictures of sitting birds, 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 telephotography.