Understanding ISO
The final piece of the photographic triangle is ISO. ISO refers to how sensitive the camera’s sensor is to entering light. Creative, interesting photographs are a result of the careful combination of aperture, shutter speed, and ISO.
Generally, the ISO settings will range from ISO 100 to ISO 6400. As digital cameras have continued to advance, higher level models may offer ISOs as low as ISO 50 and upwards of ISO 12800. A lower ISO means that the camera’s sensor is less sensitive to light, while higher ISOs results in a sensor that is more sensitive to the light.
Increasing the ISO causes a faster shutter speed, while decreasing the ISO will lengthen the shutter speed. For example, if you photographed a flower at f/4.0, ISO 100, at 1/250 sec. and then increased the ISO to ISO 200 without altering any other settings, the shutter speed would decrease to 1/500 sec.
How to Use ISO
For the most part, try to use the lowest ISO whenever possible. Increasing the ISO results in more noise in the image which can be distracting and unflattering. Unless you’re attempting to create a specific look, you will generally want to keep the ISO as low as possible. With that said, don’t be afraid to crank up the ISO if you are in a low light situation where you need the faster shutter speed. You would much rather have noisy photos than blurry photos. Likewise, underexposing a photo to get a faster shutter speed as opposed to properly exposing the photo and increasing the ISO actually makes the noise in the image worse, since noise is most abundant in a photo’s shadow areas.
In this particular image, I was forced to increase the ISO to a relatively high ISO 3200. This enabled me to capture the player during his warmup at a shutter speed of 1/250 sec (aperture f/2.8). Here, the noise actually adds a bit of mood to the photo and isn’t all that noticeable unless you fixate on it.
Low ISOs and Long Exposure Photography
Low ISOs can be used to your advantage when capturing a long exposure photo. Since lower ISOs will result in a longer shutter speed, they are a great tool for long exposure photography. They will help increase the shutter speed allowing the desired level of blur, while also ensuring very little noise in the picture. Noise is more prominent at longer shutter speeds so this helps to further combat that.
In this photograph, an aperture of f/16 along with the minimum ISO 100 led to a relatively long shutter speed of 10.0 seconds which resulted in an adequate level of blur in the middle ground of the picture and the passing clouds.
Closing Thoughts
As a general rule, use the lowest possible ISO, but remember that aperture and shutter speed should be considered first as they offer a wider range of creativity. Finally, don’t get too caught up in minimizing noise because the vast majority of the people that view your image won’t notice it.