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Photo Scrapbook (06/15/2008)
By Tom Hirsch
Using the ISO

The ISO rating in film or digital imagery is the relative sensitivity to light of the image-sensing medium. The higher the ISO number, the greater its sensitivity to light. In 35mm photography, the photographer has approximately 120 films to choose from. This includes color, black and white print films, and slide films, with ISOs ranging from 1 to 64000 or more. A digital photographer has no choice except the ISO range that came with the camera.

If you're a 35mm photographer, you might want to standardize on an ISO 400 film for general picture-taking. In digital photography, a good place to standardize is in the approximate middle of the available ISO range. But there are other films or ISO settings that you might want to consider at times.

ISO ranges are categorized by speed, as in slow, medium and fast. In film photography, slow speed films are those with an ISO number of 100 or lower. Medium speed films have an ISO rating of 125 to 400. Fast films are those with ISO ratings greater than 400. In digital photography, consider the middle of the available ISO range as medium speed, and go either way from there with regard to the following information. For practical purposes, the following jargon will be in terms of film but it also applies to digital. "Grain" in film photography refers to the coarseness of an image, usually caused by a high ISO film. This can be translated to "noise" in digital which also results in a coarse-appearing image, but with a somewhat different appearance than that of film.

As a general rule, the lower the ISO number, the finer the grain structure, and the sharper the image. A slow speed film will record with great detail the finest features in a subject. This is important when fine detail is a significant factor, as it would be in scientific work, in close-up photography, or when you want an image enlarged beyond 11x14.

For most situations in which a slow speed film is the best choice, it is strongly recommended that a tripod be used for camera steadiness. If there is any camera movement at all, it will drastically reduce image sharpness and negate the advantages of the slow speed film. When using a tripod in these situations, be sure to use a cable release. Even the small amount of camera movement that could result from pushing down on the camera's shutter release would be enough to ruin a photo. Also, the slower the film, the more possibility of blurriness from subject movement. Sometimes this is important, and at other times it's not. Blur can increase the impression of motion in action shots.

If you have a 35mm or digital camera that does not have a receptacle for a cable release but it does have a self-timer, this can be used in place of a cable release. The time delay will give the camera a chance to settle down before the picture is taken. Usually, there is a choice of 2 or 10 seconds delay. The 2 second option should be okay to use.

Whenever you want to use the panning technique, use a slow speed film so you or the camera can choose a relatively slow shutter speed, but don't use a tripod. You want as much maneuverability as possible and a tripod would just get in the way.

In contrast to slow speed films, fast films result in the coarsest grain. In digital photography, this is called "noise." In either case, it will result in the least sharp images. With film, this sounds much worse than it really is. As with ISO 400 films, the grain structure of modern fast films is much smaller than that found in previous fast films. With some of the high-quality ISO 800 and 1000 films of today, you can get very fine grain and good detail in an 11x14 enlargement, but the grain could possibly be somewhat objectionable in photos of subjects in which fine detail is important.

In an event such as a basketball game, a graduation ceremony or a circus under the big top, the distance from the camera to the activity is usually far greater than the distance range of the flash unit. In these situations, available light photography with fast film or a high ISO setting may be the only way of getting satisfactory pictures. In that case, forget about grain or noise.

For you SLR camera people, you might want to consider a variable speed film such as Kodak Gold Max for general picture taking. Although no ISO rating is printed on the film box, the basic film speed is ISO 800, but the film's extremely generous exposure latitude allows you to shoot it anywhere from ISO 50 to ISO 3200. I've tried it, running the gamut in a wide variety of lighting situations, and it works! I got very good results throughout the entire roll. For the compact 35mm photographer, Max is also a good film because of its generous latitude. 


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