The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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View Finder
utilise the camera obscura, which may be made at a trifling cost out of a spectacle double-convex lens of about i£ to 2-in. focus mounted in a brass tube, a mirror at an angle of 45 o, and a piece of ground glass on the top with a shade. In the accompanying diagram showing the arrangement, a b c d is a rectangular box of card or wood, l a lens in the mirror, g the ground glass, s movable shade, which can be raised or lowered at will. Another method is to use the focussing screen, which, when turned back over the top of the camera, should have lines drawn on it as shown in the diagram; then, when the eye is placed at a, and looking along ab, the object, when opposite this, will be in the centre of the plate. Or a double-convex lens of exactly the same focus as the photographic lens may be mounted on
Fig. 124.
the front of the camera, and the focussing cloth thrown over the whole so as to form a second or temporary camera. A new class of view finder has recently been introduced, the pioneer being Messrs. Adams & Co.'s " Bright" view finder. In this we have two positive lenses with a reflector at 450 between them, but the lenses form one doublet optical system, and form a real image near the surface of the instrument. This aerial image ean be seen very distinctly even when the object is feebly illuminated, and with the eye at a considerable distance from the finder. The u Radiant " view finder of Messrs. Marion involves the same principle, but a reflecting prism, one surface of which is ground to form a convex lens, replaces the silvered reflector and one of the lenses of Messrs. Adams & Co.'s instrument. In a somewhat similar instrument constructed by