Placing a mounted Flicker (_Colaptes auratus_) on a fence post, and setting up my tripod at a measured distance of fifty feet, a series of test exposures was made, of which three are presented as follows: First,^2 eight-inch lens (Zeiss Convertible Series VII _a_, No. 10), stop F. 8, time ¹⁄₂₅ second; second,^4 fourteen-inch front lens of the combination, stop F. 16 (equivalent to F. 4 of the eight-inch); third,^6 telephoto attachment with eight-inch lens, twenty-one-inch bellows, stop F. 8 of the eight-inch, time one second. Commenting on the results of these tests it may first be mentioned that in the “Unicum” shutter employed exposures of a so-called “¹⁄₁₀₀” and “¹⁄₂₅” seconds gave exactly the same results both with the combined eight-inch lens and the front fourteen-inch lens; the actual time, however, was doubtless not far from ¹⁄₂₅ of a second. The negatives, therefore, show, in the first place, that the long-focus lens is capable of doing fairly rapid work. Continuing our comparison, we observe that the eight-inch gives a fairly wide field, excellent depth of focus, but a very small image of the bird, for which alone the picture has been made. With the fourteen-inch we decrease the extent of the field nearly one half and almost double the size of the object pictured. This, however, has been done at the loss of depth of focus, not even the first of the line of posts running directly into the background being sharply defined, while with the eight-inch all are in focus. [Illustration: 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.] [Illustration: 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. [Illustration: 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).]