Wireless Transmission of Photographs / Second Edition, Revised and Enlarged 1919 - Marcus J. Martin

Diameter of Stop used ¹/₆₄th of Camera Extension.

Screen ruling lines per inch.	Actual space in inches.	Distance of screen ruling in inches.	In ¹/₃₂ inches	In milli- metres
35	¹/₇₀	.91	28.8	21.8
50	¹/₁₀₀	.64	20.5	16.2
65	¹/₁₃₀	.49	15.7	12.4

As it is impossible for many to have the use of professional apparatus designed for this particular kind of work,

the fixing of the screen into an ordinary camera must be left to the ingenuity of the worker. A half-plate back focussing camera will be found suitable for general experimental work, but if this is not available, a large box camera can be pressed into service.

The writer has never seen a half-plate box camera, but one taking a 5 × 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.

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

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."