. The book of photography; practical, theoretical and applied. if taken with a 10-inch lens. The disadvan-tages and costliness of such a method of ob-taining an increase in the size of the object aremost obvious, and it is these drawbacks whichthe telephoto lens overcomes. As an exampleof what can be done with a telephoto lens, acomparison of Figs. 864, 865, and 866 will beinstructive. Fig. 864 shows a view of a distantbuilding obtained with an ordinary lens ; Fig. 865 was taken from the same standpoint witha low-power telephoto attachment; while Fig. 866 was secured with a higher power, thisb
. The book of photography; practical, theoretical and applied. if taken with a 10-inch lens. The disadvan-tages and costliness of such a method of ob-taining an increase in the size of the object aremost obvious, and it is these drawbacks whichthe telephoto lens overcomes. As an exampleof what can be done with a telephoto lens, acomparison of Figs. 864, 865, and 866 will beinstructive. Fig. 864 shows a view of a distantbuilding obtained with an ordinary lens ; Fig. 865 was taken from the same standpoint witha low-power telephoto attachment; while Fig. 866 was secured with a higher power, thisbeing, however, still a small degree of magniti-. inches long would have to be employed, sup-posing it was necessary to obtain an imigeon the plate four times- as large as it would be cation compared with what could actually beachieved if necessary. General Principles of Telephoto telephoto lens is essentially a long focuslens of peculiar construction, and as it is fittedwith an adjustment whereby the focus can bevaried at will, it may fairly claim to be notmerely one long focus lens, but a series of longfocus lenses. The i)rinciples which govern theconstruction of the telephoto lens are by nomeans difficult to grasp. If a card with apinhole be substituted for the lens in a camera,and the ground glass carefully focussed, aposition will be found where the image pro- 648 THE BOOK OF PHOTOGRAPHY. jected by the pinhole is a facsimile oa thesame scale as that produced by the lens, only,of course, not so sharp or so brilliantly illumin-ated. It will be found that the position of theIDinhole to produce this effect is in the planeoc
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