e for general
experimental work, but if this is not available, a large box camera can be
pressed into service.

[Illustration: FIG. 57.]

The writer has never seen a half-plate box camera, but one taking a 5 x 4
inch plate can be obtained second-hand very cheaply. It is a comparatively
simple matter to fix the line screen into a camera of this description, the
drawings Figs. 57 and 58 showing the method adopted by the writer. The two
clips D, made from fairly stout brass about 1/2 inch wide, are bent to the
shape shown (an enlarged section is given at C) and soldered at the top and
bottom of one of the metal sheaths provided for holding the plates. The
distance between the front of the photographic plate (the film side) and
the back of the line screen (also the film side), indicated by the arrow at
A, is determined by the number of lines on the screen. As will be seen from
the table given, the distance for a screen having 50 lines to the inch will
be 41/64ths of an inch.

[Illustration: FIG. 58.

M, sheath; P, photographic plate; D, clips; S, line screen.]

In all probability there will be enough clearance between the top of the
sheath and the top of the camera to allow for the thickness of the clip,
but if not, a shallow groove a little wider than the clip should be
carefully cut in the top of the camera, so that it will slide in easily.
The screen should be placed between the clips, the film side on the {118}
inside, _i.e._ facing the photographic plate. As with a box camera the
extension is a fixture, the size of stop to be used is a fixture also. The
extension of a camera (this term really applies to a bellows camera) is
measured from the front of the photographic plate to the diaphragm, and if
this distance in our camera is 8 inches, then the diameter of the stop to
give the best results would be 1/64th of this, or 1/8th inch. Although for
all ordinary experimental work the lens fitted to the camera will be
suitable, the best type of lens for process work of all kinds is the
"Anastigmat."

The picture or photograph from which it is desired to make a print should
be fastened out perfectly flat upon a board with drawing pins, and if a
copying stand is not available it must be placed upright in some convenient
position. The diagram Fig. 59 gives the disposition of the apparatus
required for copying. A simple and inexpensive copying stand is shown in
Fig. 60. The blackboard A should be about 30 inches square, and