On cameras of this type the rising-front movements are generally limited, owing to the small size of the front and of the taper bellows. After raising (or lowering) the lens, it is necessary to centre it again before closing the camera. Closing must always be done gently, especially if one is not accustomed to this operation, for the space available within the casing is very stinted, and if all the fitments (finder, release) do not occupy the exact position assigned to them, thus preventing the baseboard from closing, any force is bound to injure some parts.
With most cameras, the front must be pushed right back into the rear body on to runners that form the continuation of those on the baseboard. When the camera is opened, it is therefore necessary to pull out the front up to the stops, which latter are usually at the " infinity " position. To do this, the front is drawn forward by finger grips on the carriage, these acting as clamps when the carriage is in position.
In the Press pull-out type, with stretcher struts, the accordion-pleated bellows is some times replaced by a leather bag completely open at the extended position. The bellows are to be preferred, for the folds stop very oblique rays not used in forming the image, and are not likely to reflect them in the direction of the sensitive surface. When opening or closing these cameras the front and the back should be kept as parallel as possible in order to avoid bending the jointed levers. Cameras with folding levers are generally opened by a slanting pull, but care must be taken that both the levers of a pair are working together, in order to prevent them from being bent.
As a rule these cameras allow of ample rise of front.
Hand cameras of the folding type are generally made in sizes up to postcard (5X 31 in.). Press cameras are made up to 61 x 4 in.
168. Focussing of Hand Cameras. With the exception of box cameras and the majority of film cameras, hand cameras are fitted with a focussing interchangeable with the slides or changing boxes and allowing of accurate focussing when the camera is used exceptionally on the tripod. But, except in the case of " reflex " and " twin lens " cameras (§ 176), direct focus sing is impossible when the camera is used in the hand. The extension of the camera must then be brought to the proper distance by means of a.
scale (§ 88) graduated in distances of the sub It then suffices to bring the bevelled edge of the pointer on to the mark corresponding with the distance chosen. 3 With box cameras, with most jumelles, and with the Press cameras, focussing is done by moving the lens in a helicoidal mounting (§ 112). In the folding cameras with lazy-tongs and " scissor " levers the variation in extension is generally obtained by restricting more or less the opening of the levers by an adjustable stop linked to a bolt actuated by a screw fixed in the rear body, the stop drawing with it the pointer placed against a focussing The range of extension thus obtainable is very limited, so that these cameras are not suitable for use with lenses other than the one which the maker has fitted. At the most, they may be fitted with a rigid or folding rear exten sion, put in place of the dark slide, which is then fitted to the other end of the extension piece. By this means it is possible to use one element of a combinable lens (§ 104) or lenses of greater focal length than that fitted to the camera.
Cameras of the folding type, especially those with double extension, afford fair scope in focussing and allow of small objects being photographed, or of the use of one element of the lens without any special accessories. It is possible, within certain narrow limits, to fit other lenses, but if that is done, it will, as a rule, be impossible to close the camera without remov ing the lens.
169. Finders. In photographing a given sub ject with a camera held in the hand, the instru ment must be fitted with a finder enabling the photographer to see whether the subject is or is not included in the useful field of the lens at the moment when the shutter is released.
The finder may be required to indicate either only the direction in which the lens is pointed. or to show exactly the limits of the field in cluded. Let us hasten to add that in many of the cameras at present made the finder does not merit the confidence that one is led to place in it, so that the checking of the finder is a neces sary precaution with any camera.
The problem of the finder is, moreover, a somewhat complex one if it is desired to solve it with desirable precision.