What ISO Is and How It Affects Your Digital Photography

ISO represents your image sensor's sensitivity to light. The higher it is, the greater the sensitivity. For beginning photographers, increasing the number may seem to be an intuitive approach in low-light environments. This is especially true when taking shots in situations where using a flash is prohibited or less than ideal given your subject (e.g. portraits). The problem is, as with most of the settings on your camera, there's a tradeoff to using ISO.

This article will explain how ISO affects your photographs. We'll describe some of the compromises you'll need to make when increasing the setting, and the circumstances that might require you to do so. You'll also learn which factors to consider when selecting the proper setting for your photo posters.

When there is no light source, or available light is limited, your camera will adjust the shutter speed to compensate (in auto mode). By slowing the shutter speed, the image sensor is exposed to available light for a longer period. The tradeoff is blur. With the shutter opened longer, any element in your shot that is moving will appear blurred.

The most obvious solution for reducing blur is to increase your camera's shutter speed. However, this limits your image sensor's light exposure, which means you'll need to find another source if you're shooting in low-light situations. One possible alternative source is a flash.

The problem with using a flash is twofold. First, as noted earlier, using a flash may be inappropriate if you're taking portrait shots or photographing within an environment that prohibits the use of flashes. Second, a flash may be insufficient as a light source for the setting (e.g. a dimly-lit cavernous hall). Another solution is to increase the ISO.

Because this feature raises the image sensor's sensitivity to light, you can increase the shutter speed. This helps eliminate the problem of blur. It also means you can produce clearly-lit photographs without needing to use a flash. But there is a tradeoff.

 The biggest problem with increasing your ISO setting is image noise. The image sensor's increased sensitivity to light introduces a grainy texture to your photos. The grain may not be obvious. If you're looking at your images through your camera's LCD viewfinder, you're unlikely to notice it. However, once you print your photographs or upload them to your computer, you'll see the grainy texture (and so will others).

Circumstances That May Require A Higher ISO

Given the compromise you're forced to make when using a higher ISO (i.e. image noise), when might doing so be necessary? First, any situation in which your subject is moving and there is very little light available might require it, especially if a flash cannot be used.

Second, consider environments that invite photography, but are dimly-lit and prohibit flashes. This includes museums, weddings, and art exhibits. Using a slower shutter speed to compensate for the lack of light will introduce blur due to camera shake, even if your subjects are stationary.

There are, of course, countless other situations for which increasing the ISO represents the best solution, despite the tradeoff in image quality. For this reason, it's worth establishing a few easy-to-apply rules to guide your decision.

 The first issue to consider is the size of your final product. If you're planning to transfer your photographs to large prints, image noise will be more noticeable. Smaller shots, however, can accommodate a higher ISO with little effect on the viewer.

Also, if you're using a tripod, you won't need to worry about camera shake. This means you can slow the shutter speed rather than increasing the ISO to compensate for low-light settings.

Motion is another key factor to consider. If your subject is stationary, your image is less likely to blur as the result of using a slower shutter speed. Thus, balancing the shutter speed with a higher ISO may be an ideal approach for improving your photograph's quality.

ISO is a valuable tool when shooting in low-light environments. Learn to use it as one of many ingredients (i.e. settings) in producing high-quality, well-lit images.