Beginner's Guide: ISO Settings in Digital Photography

Photography is built on the 3 pillars of exposure: shutter speed, aperture and sensitivity.

Shutter and aperture are controls for adjusting how much light comes into the camera. How much light is needed is determined by the sensitivity of the medium used. That was as true for glass plates as it is for film and now digital sensors. In traditional (film) photography ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (The "normal" range of ISO is about 200 to 1600). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking.

In digital cameras, raising the ISO means a similar decrease in quality, with an increase in what's called "noise." It's the digital equivalent of grain and results in a sort of "chunky" look to the image.

One important factor affecting the amount of digital noise in an image is the size of the pixels used on the sensor. Large pixels result in less noise than small ones. That's why digital SLRs perform much better at high ISOs than compact cameras. The SLRs have larger sensors and larger pixels.

Another factor is the amount and type of noise reduction being applied in the camera. Because all pixels collect some noise, every digital camera runs processing on every image (although with a NEF, or RAW, file that can be changed later) to minimize that noise. Newer cameras use newer technology to reduce that noise, with the result being less noise at similar ISOs than what earlier cameras could achieve.

Higher ISO settings are generally used in darker situations to get faster shutter speeds. However the higher the ISO you choose the noisier shots you will get.

A lower ISO will usually produce more color-accurate, aesthetically pleasing images, but there are situations where a higher ISO is desirable. The proper ISO setting really depends on the level of lighting you’re shooting in and the visual effect you’re going for.

Auto ISO was introduced into digital cameras to help photographers manage that balance. Turning on that feature allows the camera to push the ISO up when it decides the shutter speed is getting too low for a good picture. Even better, newer Nikon cameras have added "ISO Sensitivity Auto Control" to the menu choices.

This takes Auto ISO and lets you have some say about what happens. Using it, you set the limit for how high it can go (800? 3200?) and at what shutter speed it should start raising the ISO (1/125? 1/30?). The amount of control this feature allows means more photographers will start taking advantage of it.

Most people tend to keep their digital cameras in ‘Auto Mode’ where the camera selects the appropriate ISO setting depending upon the conditions you’re shooting in (it will try to keep it as low as possible) but most cameras also give you the opportunity to select your own ISO also.

When you do override your camera and choose a specific ISO you’ll notice that it impacts the aperture and shutter speed needed for a well exposed shot. This means photographers are constantly doing a balancing act. They want to keep their ISO low for high quality images (low noise), but also they need a fast enough shutter speed to get a sharp picture. That's why there's such high value placed on groundbreaking cameras that allow photographers to shoot at higher ISOs with less noise than ever before.

An understanding of ISO will help you make smart decisions about how to set your camera. And that, in turn, will lead to better pictures. Experiment with different settings and how they impact your images today...!