153. Studio Portrait Cameras. As these cameras are never used outside the studio, considerations of weight and bulk are altogether secondary to those of stability and rigidity, and of precision in manipulation. The camera is usually of the triple-body type, so as to allow, if necessary, of the copying, enlargement, or reduction of negatives and transparencies. The long extension of a triple-body camera permits the use of lenses of long focal length when required. When a long extension is not needed the front part of the camera acts as a lens shade, which is an indispensable accessory in a studio, where the great volume of light from walls and roof may cause general fog on the image as a result of multiple reflections within the lens. 1 he size of plate accommodated by a studio camera is never less than 81 x 61- in., and rarely exceeds 12 X '0 in.
In either of its positions (on the middle body or on the front body) the lens must be fitted with a considerable amount of rise and fall, the height generally chosen for it being at the level of the sitter's eyes. The camera back is usually fitted with a vertical swing. This per mits of a large lens aperture being used, and yet of uniform sharpness being obtained throughout the image of a seated figure, the knees and face of which are at very different distances. It also allows of the plate being brought into a vertical plane when the front of the camera has been pointed downwards, as in photographing a child, who is often best photographed from some height, that being the position from which a child is usually seen.
The dark slides are generally of single pattern with a curtain shutter, of square shape, and fitted with a series of rebates to take the plates either way ; also with sets of carriers. Modern slides are often fitted with devices enabling either glass plates or flat films to be used at will. The focussing screen is marked, usually in pencil, with the outlines of the different sizes in common use.
The repeating back with which a studio camera is usually fitted enables two or more negatives to be made in succession on the same plate, and allows the focussing screen to be quickly replaced by a slide, the shutter of which has already been drawn. The repeating back is interchangeable with slides of the full size of the camera, and consists of a board with slide bars accommodating a frame that can be pushed along them until checked by stops. This frame takes dark slides of 6 x 4-2 in. (in the United States, 7 X 5 in.) or 8i x 61 in., and a focussing screen is permanently fixed at one end of it.
Velvet light-traps half-embedded in this sliding frame prevent light from reaching the plate after it has been uncovered. In the centre of the board there is an aperture of the dimensions of the plate (sometimes with a detachable mask for another size). Notches placed at the proper points of the slide-bars automatically engage with a spring-bolt fixed on the sliding frame.
For easy working it is necessary that the dark slides should be sufficient in number to obviate having to unload and refill them too frequently.
The focussing cloth, which is needed for inspecting the image on the screen, must be of perfectly opaque material (very close cross weave) and of ample On some cameras the cloth is supported by a light metal frame fixed to the back of the camera and forming a kind of hood which keeps the cloth clear of the operator's head. Not only is this arrangement a more comfortable one, especially in hot weather, but it is required by elementary hygienic reasons where several operators are likely to follow each other at the same camera. Portrait cameras are sometimes fitted with a vignettes (Nadar, 1863), which enables the picture of the bust of the sitter to be limited by a gradual shading off into the light or dark tint of the background. For vignettes against a dark background an opening of appropriate shape is cut out of black, matt-surfaced card, and fixed inside the camera between the lens and the plate, far enough from the latter not to cast a sharp shadow. For vignettes against a light background, a similar aperture is cut out of white card, generally with a serrated edge, and this is held in front of the camera, inclined at an angle such that the surface of the card is well lit, Rods passing beneath the camera enable the operator to regulate at will the distance, height and tilt of the vignette while about 33 per cent more than the minimum height to which it can be lowered. The arrange ment is very stable and is still used for certain branches of commercial photography. But for portraiture it tends to be replaced by an arrangement giving a larger range of movement. In this there is a table or top, carrying the baseboard of the camera, which top can be tilted on a horizontal axis. The table moves up or down between two or four pillars fixed to a base. Pinions fixed beneath the table engage with racks on the insides of the pillars which sometimes contain counterweights. The top can following the result of these adjustments on the focussing screen.