In the old days of photography, especially with the SLR camera, "film" was used to capture photographs. This photographic film was little more than a thin sheet of plastic (film) coated with a photosensitive emulsion, and wrapped around a roller. The entire assembly was encased in a light-proof canister (a roll of film). As pictures were taken, the roller was advanced and the exposed film held on a second internal camera roller. When all the available exposure space on the length of film was exhausted, the spool was rewound back onto the original spool and sent for developing.

The photosensitive emulsion used on photo film had a specific sensitivity to light that was a combination of sensitivity and density of the emulsion coating. Less sensitive film with a correspondingly lower speed index, required more exposure to produce the same image density as a more sensitive film, and was commonly termed as a "slow film". Highly sensitive film was termed "fast film". Since the slow film had less sensitivity, it usually had a higher density of emulsion coating. This produced a much more vibrant image with greater detail. Faster film had less density of emulsion coating, and while this allowed for faster collection of light to form the image, also resulted in "grain" within the picture (unclear photo).

In film photography, slower film such as ISO 64 or ISO 100 was used for studio or portrait photography. Since the subjects were relatively motionless, a longer exposure time coupled with adequate lighting resulted in superbly clear and vibrant pictures.

Faster film speed was necessary for fast moving or active subjects, such as sports photography. ISO 1000 or even upto ISO 3200 were used to freeze the action onto film. For normal use, a midrange speed such as ISO 200 or ISO 400 would provide reasonable clarity with sufficient speed for normal activities or outdoor shooting.



The SLR camera had to be adjusted to the "speed" of the film being used, since the amount of light (aperture) and exposure time (shutter speed) had to compensate for the film ISO speed. Some advanced photographer tricks include "pushing" the exposure (setting the ISO to a higher setting than the actual film being used), or "pulling" the film (setting a lower ISO setting than the actual film). These tricks resulted in deliberate over or under exposures, which when coupled with deliberate manual settings of aperture and shutter speed, resulted in unique photographs that the photographer desired to achive.

Digital SLR cameras use a photosensitive CCD element that simulates the film from days past. Similar to film exposures, the amount of light that is recorded by the individual pixels on the CCD sensor can be manipulated to simulate the ISO film speed. DSLR cameras thus have an ISO setting that works in exactly the same way as the old fashioned photographic film.

Setting a lower ISO film speed provides crisper images, since the CCD has more time to collect light and render the image in more detail. A higher ISO speed setting with a faster shutter speed allows the camera to capture the image faster, but there is quality loss that results in the exact "grain" such as that from high speed traditional film.


All DSLR cameras have a "native" minimum setting. They also allow for lower settings, but these are simulated by the onboard computer. This forced low-ISO setting usually results in weird looking images and color shift, since the camera computer is interpolating extra detail between the existing CCD pixels. While this can make for some interesting photos, it is generally more of a nuisance than a useful feature.

Most DSLR cameras also have an "auto ISO" feature. This may or may not work in every case. The onboard computer attempts to identify the subject type that you are shooting, and will dynamically switch to a suitable ISO speed that it thinks is appropriate. For example, if the auto focus is rapidly compensating the focus, it is probably a fast moving subject and therefore the ISO should be higher. Or the reverse, if the focus is locked and the light level is high, it may be a portrait so a lower ISO setting is used. Computers are smart, but not that smart. It is always better to set the ISO speed manually before shooting. You know about the subject you intend to shoot, the camera doesn't.


While the clearest photographs can be achived with a lower ISO speed setting, it also can result in blurry pictures. Since the CCD requires more time to collect light to form the image, you will be using a slower shutter speed, therefore a longer exposure time. Between hand shake (yes, anyone's hand can shake holding the camera and lens) and vibration due to the autofocus mechanism, or even a passing car; the most perfect photo opportunity can be ruined. The use of a tripod is definitely recommended wherever possible.

And yes, tripods can be bulky and a pain to carry around, but its a small inconvenience when compared to losing the shot (blurry pictures) or sacrificing clarity (using a faster ISO or shutter speed to compensate for vibration/shake). The Monopod is an interesting middle ground. Just as a tripod has three legs (tri); the monopod has just one leg (mono). You can't leave a monopod by itself, it will fall over. But similar to a walking cane it provides a rest as well as cushioning for the camera and lens. You simply hold the camera as normal, but the weight rests upon the monopod, not on your hands. And most monopods also collapse into a compact size; making it easy to carry, stow, or simply leave attached to the camera.

Digital Photography Aperture & Shutter Speed Settings<<<Previous