Camera ISO is one of three settings you must understand to create great exposures. These are the basics that should become engrained in your head so well that you know what to do without even thinking.
In the olden days, back when Journey was performing “Don’t Stop Believing” for the first time, or the Beatles were still performing, ISO was the sensitivity/speed of the film. It used to be that photographers had to change the roll of film to change the ISO. Glad we got into photography when it went digital! What it means is how sensitive the film is to light. The higher the ISO, say 400 or 640, the more sensitive the film was to light meaning that a smaller aperture and quicker shutter speed could be used to get the same exposure.
Now, much like the days of film, ISO refers to how sensitive the camera’s sensor is to light. Simply adjust the setting on your camera to whatever ISO you want, and click away. For action shots, it’s often necessary to crank the ISO up to get a properly exposed image with a fast enough shutter speed. It also allows you to stop down your aperture to get an image that has larger depth of field (How large a slice of the image is in focus.)
However, there are some drawbacks to cranking the ISO up, and all cameras react differerently so it’s important to test yours at different settings. The higher the ISO, the more detail is lost in the image. With modern cameras this is not nearly the issue it used to be and the ISO can be cranked up all the way to 1600 or 3200 before this becomes an issue. The other drawback is that the image will gain more grain to it and look less sharp, this grain is called “noise” and can be reduced later with post-processing, but at a loss of some detail and sharpness. Again, experiment with your camera by shooting the sky at different ISO’s and find out how far you can push it before the image is “unusable”.
The lesson to be learned? New cameras allow you to shoot fairly high ISO’s with minimal drawbacks. Find out what the limit is for yours and stay within that range. Shoot lower ISO’s whenever possible to create the sharpest and least noisy images you can. But don’t be afraid to turn it up if the situation requires doing so.
Next Guide Article: Shutter Speed and Action Explained