ISO can be a very important tool in digital photography. It allows you to capture great images in low light when used properly, yet without a firm grasp on the limitations of your equipment, it can very easily ruin your photos. Most digital cameras allow for manual over-ride of auto-ISO. Learning to master when and how to use ISO will be an important step to improving your photographs.
Light is one of the most important aspects in photography. Too much light and your photos may look harsh with deep shadows and loss of detail in both the highlights and the shadows. Too little light and the camera sensor may struggle to view the image leading to difficult auto focus, blurry photographs, or heavy grain. Luckily, using the ISO can help us overcome some of these challenges.
ISO allows you to increase the gain in your camera to see in lower light situations. Unfortunately, this increased light sensitivity comes at a great cost. Depending on your camera, the image will begin to show grain and loss of detail as your ISO increases. This will lead to poor results on your image, especially when viewed at 100% or in large prints. In almost all circumstances, shooting at the lowest ISO possible will produce the best results. At the same time, while we may tolerate some grain in the image, a photo show at too slow of a shutter speed, for example, that produced motion blur, will most likely be unusable. That said, while we strive to achieve a low ISO, it is better to increase your ISO than risk shooting at too slow of a shutter speed or too wide of an aperture.
Knowing your camera is a very important part of this equation. While some cameras like Nikon’s D3s have been known to perform well at over 6400ISO, other cameras like most point and shoots will produce noticeable grain and loss of detail at 800ISO or less. There are a couple factors that can lead to poor results at high ISO and among them are sensor size and pixel count. Contrary to the marketing push, more pixels are not always better. When you pump extra pixels on the same size sensor, you often make grain more prevalent and it is very difficult for the camera to produce great results at high ISO settings. This is why some of the top cameras for low light such as the Nikon 3Ds contain only 12 megapixels on a full frame sensor. As the camera sensor gets smaller such as in point and shoot cameras, its sensitivity to light changes and the camera is less able to see in the dark. Combine that small sensor with extremely high pixel counts, and you have a recipe for poor low light pictures. DSLR’s typically perform well in low light due to their large sensors. Most inexpensive consumer dslr cameras such as the Nikon 3100 and Canon T3 yield perfectly usable results at up to 1600ISO and sometimes up to 3200ISO. Knowing how your camera performs will let you know what limits you need to impose on your camera settings to make sure you are getting the best results. I encourage you to take a picture at different ISOs to learn at what point grain and loss of detail are prevalent. It is also important to know where your picture may end up. While a small size picture on the internet may not show grain, that same picture printed at 20x30” may look horrible. If you plan on professionally printing your picture, you may want to place tighter restrictions on your ISO limits.
Typically on most cameras, the difference between 100ISO and 400ISO is almost negligible in many pictures. As a result, I may be very quick to increase my ISO up to 400 if I feel fast shutter speeds or narrow apertures are important. But when the situation requires high ISO settings to achieve low light results, I pay very close attention to this setting. Learning to prioritize your settings is the important next step to mastering ISO. If you are taking a picture of a moving subject, motion blur may very quickly ruin your photo while some grain and loss of detail is tolerable. It is for this reason the importance of mastering ISO cannot be overstated. Your cameras AUTO mode is not able to prioritize these settings for you and thus may leave your ISO high and your shutter speed fast while taking a picture a non-moving house on a tripod mounted camera. At the other end, you may want to capture quick movement while your camera sacrifices fast shutter speeds for low ISO. Knowing how to set your ISO will lead to much better photos in almost all circumstances.