What is auto ISO and how can it help you?

When we’re shooting images, we often prefer to choose the shutter speed or the aperture and leave the ISO number to be manually set. Sometimes we don’t even tinker with the ISO setting and leave it at its lowest number. This can hurt us at times. Especially now when cameras can shoot clean images even at higher ISO numbers. Let’s take a few examples to understand the problem.

Let’s say you’ve set your aperture at f/8 and the shutter speed at 1/100 sec. You’re shooting with a wide-angle lens and need a considerable field depth to ensure that your image appears sharp across the frame.

The problem is that at f/8 and 1/100 shutter speed, although you’ve taken care of the depth of field and considered the low light situation to ensure that you have a clean image that’s well exposed, you haven’t considered image shake.

At 1/100, you could be dangerously close to the optimum shutter speed with an 85mm or a 100mm lens. Maybe not so much with a 35mm or a 24mm lens, but when you attempt something like that using a more minor, more extended focal length image, shake comes into the picture.

You can easily take care of this by dialing a higher ISO number. A higher ISO number will compensate for the faster shutter speed or, the slower aperture. But that’s one more parameter that you’ve to dial manually. Is there a way that the camera can dial in the ISO on the fly whenever you’re close to the danger zone with your shutter speed? The answer is yes. The solution is Auto ISO.

Auto ISO is a feature that you activate manually. You set the highest ISO number you’re prepared to use and the slowest shutter speed when Auto ISO should kick in, and the camera does the rest.

Let’s say you choose an aperture of f/5.6 and a corresponding shutter speed of 1/100 sec. If the camera feels too fast at a shutter speed, it will automatically trigger the ISO parameter and set an ISO number that will compensate for the lack of light. Say, 1/100 is a reasonable shutter speed. But you push it even further. You select a shutter speed of 1/200. Aperture, however, remains the same. At that time, the camera will push the ISO even higher.

Is there an upper threshold limit to what the ISO can go? Yes. This will depend on the higher ISO level that you select. This will depend on the noise level your camera produces at higher ISO levels. If you select ISO 2000 to be the highest number, then that’s the highest that the camera will set on its own and won’t go beyond it.