Lesson 15 : Processing of Film in Conventional Photography
Photographic Characteristics
ASA rating/speed This is a rating, by the manufacturer, of the particular film's relative sensitivity to light. Another term for this is the film's speed. Films are rated as slow (ASA 25-75), medium (around ASA 100-125), and fast (ASA above 125). So, the higher the ASA number the faster (and more sensitive to light) the film. When you set the ASA number on your camera, usually by adjusting a dial on the top left of the body (or letting the camera automatically set it for you), you are telling the meter how fast your film is. So the first step to good exposures is setting the ASA on your camera correctly.
Contrast In general, the slower the speed of the film, the more inherently contrasty it is. Thus, a 100 ASA film is more contrasty than a 400 ASA film. This characteristic can be controlled/manipulated by developer, developer/time combinations and agitation during development.
Grain Grain refers to the ability to see individual bits of silver. A grainy image simply lacks crispness. Excessive grain looks fuzzy. As for film, the slower, the less inherent grain. Grain is quite important with 35mm photography, as making even an 8 x 10 inch print requires quite a bit of enlargement—some 50x—whereas an 8 x 10 from a 4 x 5 inch negative only needs 4x. Grain can be manipulated in development like contrast.
Exposure Latitude Exposure latitude is a film’s ability to be under- and over-exposed, and still produce a printable image. In general, slower films have less latitude than faster films, black-and-white films more than color, and transparency films (slide film) very little at all.
Acutance Acutance is a measurement of a film’s ability to record edge sharpness, particularly between differing tonal areas. Slow films do this better than fast films, producing more appprent sharpness in the image. Acutance is actually measured by photographing a knife edge.
Resolution Resolution is the ability of a film to resolve detail. Related to acutance, resolution is measured by photgraphing tightly-spaced horizontal lines. High resolution film can ‘see’ several hundred lines per millimeter, low fewer than fifty. Grain structure, exposure and development all play a role in resolution.
Characteristic Curve A characteristic curve is a graph of density vs. log exposure for a particular film/developer combination. What this means in English is that a characteristic curve gives you an idea of how a film reacts to a given exposure and a given developer.
The characteristic curve consists of a toe—film base + fog desity, a straight-line portion, and a shoulder—where density reaches D-Max. It can be looked at as a cross-section of the film, the least exposed is the thinnest, and most the thickest. The angle of the curve is an indication of contrast, with a steeper curve meaning more contrast.
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