Shooting in a situation in which the available light changes from one shot to the next? Then you might want to try auto ISO.
In digital cameras, “ISO” equates to the sensitivity of the camera’s digital sensor to light. So, the lower the ISO number, the less sensitive your camera’s sensor will be to the available light. Conversely, increasing the ISO number increases your camera’s sensitivity to light. Modern digital cameras allow you to quickly change the ISO number from shot to shot depending on your requirements. The downside is that the higher your ISO setting the more noise the resulting photograph will likely have. If it has too much noise, the photograph can appear grainy and distorted.
So, as a general rule, you’ll probably want to keep your ISO as low as possible. For example, if you are photographing a landscape on a bright day, then you would be best to set your ISO as low as your camera will allow. On the other hand, if you are trying to capture birds or animals in a forest on an overcast day, then you may want to increase ISO to make more light available to your camera’s sensor.
When To Try Auto ISO
Most modern digital cameras have an auto ISO setting. As the name implies, this setting automatically changes the ISO number based on the light available to the sensor at the time you take the shot. So, the ISO will adjust itself up or down for each shot without you needing to change anything. And, there are situations in which enabling auto ISO can help you get better results.
For example, on a recent photo shoot, I was snapping pictures of everything from lizards scuttling along in the undergrowth to birds perched in high trees or flying against a bright sky. And, to best capture moving subjects, I had my camera in shutter priority mode and set to a quite high shutter speed. For the bright sky shots, I could have both a high shutter speed and a low ISO. But, to capture moving subjects in the darker environments, I needed a high shutter speed coupled with a higher ISO to provide more light. This is a perfect scenario in which to try auto ISO.
Instead of needing to stop and adjust ISO between shots, I just let auto ISO handle the changes for me.
Exactly how to enable auto ISO will depend on the make and model of your camera. But it will likely be in the ISO sensitivity section of your camera’s settings menu. You might need to dig out the dreaded manual.
Limiting Auto ISO
As noted, high ISO settings can substantially increase the noise in your photographs. And, left unfettered, auto ISO might sometimes ramp up the ISO to the point at which there is so much noise that the image is effectively ruined. However, you can easily counter this problem by specifying the maximum sensitivity (highest ISO number) that you want auto ISO to go to. You’ll get to know at what ISO number photographs taken with your camera become unacceptably noisy. You can then limit auto ISO so that it does not exceed this ISO number.
Don’t Forget to Turn off Auto ISO
So, auto ISO can certainly be handy in some situations. However, it’s probably best to avoid having it it enabled all of the time. Especially if you are still learning (as I am). Manually adjusting ISO as you go can help give you a deeper understanding of how your camera interacts with available light. And, to avoid unexpected results, it’s probably best to leave your camera at its lowest ISO setting by default. Thus, if you do try auto ISO, it’s a good idea to turn it off again after your photo shoot.