Photographic optics and colour photography : including the camera, kinematograph, optical lantern, and the theory and practice of image formation / by George Lindsay Johnson.

  • Johnson, G. Lindsay (George Lindsay), 1853-1943.
Date:
1909
Catalogue details

Licence: In copyright

Credit: Photographic optics and colour photography : including the camera, kinematograph, optical lantern, and the theory and practice of image formation / by George Lindsay Johnson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    and made to hinge against either the long or the short side of the focussing glass.1 § 5. Reflex Camera.—2. By a moveable mirror hinged inside the camera body.—A reflex camera, which is one in which the mirror is inclined at 45° inside the camera, and the ground glass is fitted horizontally into the upper part of the apparatus, effects the same result as the last method, the image being likewise laterally inverted. The mirror is backed by a blackened board which faces the sensitive plate. This board lies right against a flange (except during the exposure of the plate), so that no light can reach the latter. As the distance from the axis centre of the mirror to the centre of the focussing screen is exactly equal to the distance between the centre of the mirror and the plate, it is obvious that if the image is sharply focussed on the screen it will likewise be in focus on the plate when the mirror is raised (see Fig. 12). To make an ex- posure, the shutter (which is preferably a focal plane one, and made of black twill) is first drawn over the plate and adjusted to the desired speed. The object is then focussed on the screen. By pressing a release catch, the mirror swings up by means of a spring, and in the act of rising, releases the shutter-blind, which passes down over the plate. The exposure is effected by the horizontal aperture in the blind which traverses the entire length of the plate. The mechanism is so adjusted that the exposure is completed before the mirror strikes against the roof of the camera, which otherwise would cause a jar. This form of camera is a great favourite with many amateurs, its chief objection being that it cannot be folded up like a bellows camera. Newman & Guardia, Eoss, Watson, Shew, Marion, Beck, Sanders & Crowhurst (Fig. 9), Sinclair, Adams, and many others make a speciality of it. Sanders' instrument has an unusually long extension, and is extremely rigid. The image can be seen (full size) both on the top and in a line with the object. It is made for hard and rough work, and is not likely to get out of order. Dallmeyer was the first to adapt the telephoto lens to the reflex camera, and his model is largely used by naturalists (Fig. 10). The long extension renders focussing difficult in 1 Those who have not tried this plan will be agreeably surprised to find how the mirror assists in composing a picture, especially in portraiture. Messrs. Perken & Son carried out my ideas in a way that leaves nothing to be desired.