I have been asked by Mick, on my post showing an example of noise, how do you know if your ISO is set too low?
A good question. The idea with ISO is to keep it as low as you can to get the best image quality, but setting your ISO too low will mean that your shutter speed might need to be too long in order to get the correct exposure.
So let’s say that you are doing sports photography where you need a fast shutter speed to capture the action, and you are already using the largest aperture you can but you still can’t get a sharp image. Your ISO is set to 100 to get good image quality but the fastest shutter speed you can achieve is only 1/60th of a second which is not quick enough. This is a situation where your ISO could be said to be too low.
If you set the ISO to 200, which should still give you a good quality image, you can then get a shutter speed of 1/125th of a second, twice as fast which should help a lot to freeze the action.
So Mick, hopefully that explains when your ISO is set too low, when you can’t achieve the shutter speed or aperture settings required at the current ISO setting.