Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon (1908)
Hildebrandt, A. (Alfred), b. 1870, Story, W. H. tr · New York, D. Van Nostrand company · leaf 342
y now be well to consider why telephotographic lensesare not employed under all circumstances. The reason is thatthe image is not so sharp, and the intensity of the light whichfalls on the plate is reduced. If two lenses, each of a focallength of 8 in., are placed one behind the other, and the… … Fig. 197.—Diagram showing the relation betweenthe focal length of the lens, the size of the image,and the distance of the object. 318 AIRSHIPS PAST AND PBESENT. only be used in moderately clear weather ; in dull weather theybecome useless, because under such conditions and with suchlenses…
Aeronautics
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