Line Photography

Line photography is the least difficult of the three general groups of products into which graphic-arts photography is divided. It is used to produce negatives from black and white copy that does not contain intermediate or gray tone values.

The steps necessary to produce a line negative are: (1) Place copy in copyboard, (2) set camera to correct focus, (3) load camera with film, (4) make exposure, (5) process exposed film, and (6) inspect finished product.

Copy.—The quality of copy is determined by considering the image color, background, and line-image quality. Copy color is important in order to determine whether the use of a filter will be necessary. The actual line image itself should be carefully examined to determine fineness and blackness of letter characters.

Camera setting.—The lens apertures, use of filter, lights, and camera setting for proper size are the main considerations involved. For line work, the most common lens openings at same size are F 32 and F 22, as most process lenses have their best definition and resolution at these apertures. Cameras are placed in focus by two methods: (I) manual focusing by the use of hand cranks at the lens board and copyboard which are turned until a pointer on each unit indicates the percentage scale desired, and (2) mechanical focusing which provides motored transport for lens and copyboards. This system uses a counter and is calibrated for each percentage of reduction or enlargement to correspond to a certain counter number. Cameras can be focused at the camera back station or the lens board station. If a specific dimension must be measured on a ground glass at the film plane, the focus adjustment must be made at the camera back.

Exposure.—Most exposures are made using a fixed aperture and varying exposure time according to type of copy and size. An average exposure of 25 to 40 seconds is required for lithographic film.

Processing.—The result of exposure is the formation of a latent image. The latent image is made visible by chemical development. In line photography the two controlling factors for development are agitation and temperature. The recommendation received with most film is for 68 ° temperature and a development time of 2 1/4 to 2 1/2 minutes.

Inspection.—After development, the negatives are inspected and any correction due to overexposure or poor copy is made by using Farmers reducer, which is composed of potassium ferricyanide and sodium thiosulphate in a water solution. Portions of letters which are weak may be made clear on the negative with this solution.