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CAMERA APPLIANCES 139
in the meantime being kept perfectly rigid with its baseboard horizontal, thus avoiding faulty pictures due to want of verticality in the plate. It can be readily understood that the more or less parallel perpendicular lines in any object, e.g. a church tower, would not appear as such in any picture produced upon a plane which was itself out of the erect position ; the swing back, and now the rising and swing front, are designed to avoid this error.
A good camera is so built that it is perfectly rigid when at full extension, and the rack and pinion by which the baseboard is extended works smoothly and easily. There may also be a further rack and pinion by means of which the back is racked forward on the base-board so that the camera can be used with a short focus wide angle lens if desired.
The front must be so arranged that the lens is capable of a side-to-side motion.
The back of the camera should be made so that the plate can be used with its long side vertical or horizontal as required, and the double dark slides should fit easily into the back, the whole being absolutely light-tight when the plate is ready to be exposed.
The stand, while being made as light as possible, should be absolutely rigid, and a turntable likewise be provided with it, so that the camera can be swung round in a horizontal plane to point in any desired direction. Lastly, the whole should be easily packed in a relatively small space, and also easily and quickly unpacked and arranged when required for use.
Some arrangement such as a small spirit level or other suitable contrivance should be attached to the back of the camera in order that the back may be in such a position that the plate to be exposed is held in a vertical plane. Of course the wood of the camera should be such that it does not warp or crack, and so admit the light. Special precautions in this respect are necessary in cameras de