The American annual of photography . uickly exchange lenses when the occasion have found the beautiful Adon Telephoto lens of invaluableaid in securing pictures of nests, their contents and their build- 368 ers in tree tops, cliffs, across small streams and other inaccessi-ble places. This lens consists of a 4^ positive element and a2 negative element, giving a ratio of 2^ and a separation ofthe segments of It works at F/15 with a bellows exten-sion of 6 inches. The lens is complete within itself, givinggood illumination, thus permitting easy focusing. At a 5 ex-tension it gives
The American annual of photography . uickly exchange lenses when the occasion have found the beautiful Adon Telephoto lens of invaluableaid in securing pictures of nests, their contents and their build- 368 ers in tree tops, cliffs, across small streams and other inaccessi-ble places. This lens consists of a 4^ positive element and a2 negative element, giving a ratio of 2^ and a separation ofthe segments of It works at F/15 with a bellows exten-sion of 6 inches. The lens is complete within itself, givinggood illumination, thus permitting easy focusing. At a 5 ex-tension it gives a focal length equivalent to an 18 lens anda 3 linear magnification as compared to a 5 lens. To get the equivalent focus of any bellows extension, mul-tiply the extension by the ratio of the negative lens (2) tothat of the positive (4 J-^) equal to 2^ and add the focallength of the positive. For instance at 14 inch extension,14 X 2^ =311^ -|- 4!/^ = 36 equivalent focus. To findthe F value at this extension divide the focal length by. Figure SHRIKE OR BUTCHER BIRD. 5/6 — 36 -i- 5/6 = 30 F. To determine the magnificationas compared to a j lens, divide the equivalent focus by 6,36 -i- 6 = 6. In bright light this lens requires at a 14 inchextension using the 8 stop marking, about one second on ordin-ary landscape views. Of course a longer time on near ob-jects. The time of exposure as indicated by Wynne meterbeing the same as that for any other lens of equal focal instance, a plate with an F Value (Wynne) of 90; timeto color (Wynne meter) 4 seconds. At a 14 inch extension ofbellows, Adon opening (equivalent to F/30) the time wouldbe Yi second meter reading for F/32, while for the Adon ifstop 4 were used, the time would be four times as long or twoseconds. 269 A long focus lens as a rule is better for this work, yet ashort focus, 5 or 6 inches, gives depth of focus and detail* without stopping down very much, the longer focus giving alarger image. In many i
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1919
