ISO: Varying Your Camera’s Sensitivity To Light, Varying Noise
Increasing the ISO makes the camera’s sensor more sensitive to light. That means the camera can capture images in darker places or at faster shutter speeds or smaller apertures. But noise increases as ISO increases. That means quality decreases, sometimes to the point that photos are as much noise as they are image.
In general, ISO can be adjusted manually in the following shooting modes: P, Tv or S, Av or A, and M. In many cameras, ISO cannot be set by the user in the Green Automatic mode. In that mode, everything stays automatic, including ISO.
NIKON USERS: In some Nikons, the Auto ISO has to be turned off and only then can the ISO be adjusted manually, two separate operations.
To test a camera’s ISO settings, start with the lowest ISO and double it each shot up to the maximum ISO setting. Then look at the images to see how the image quality gets worse as the noise increases. QUESTION: What is the highest ISO setting that still produces acceptable results? If your camera can go to ISO 25,600 but you do not like the looks of images taken above 3,200, then ISO 3,200 is your working limit.
ISO: Varying Noise
Changing the ISO setting on your camera also controls how much noise is in your images. Noise is like film grain, like someone sprinkled salt and pepper on top of your image. Noise can also produce odd blobs of red, green, and blue. See the examples below.
Newer cameras do a much better job than older cameras controlling noise. They also allow for much higher ISO settings, 102,400 and higher.
100% closeups of photos taken with a DxO One camera at varying ISO settings, pixel-for-pixel.
Below are small portions of the photo of the ivy on the fence. These are pixel-for-pixel, 100%, of photos taken in September, 2018, with a DxO camera. As ISO increases, the shutter speeds get faster, making the images sharper as camera shake is eliminated. But then, as ISO increases further, the noise becomes ugly.