When to change the ISO
There are so many ways to change the exposure on your DSLR that it's easy to get lost on a sea of possibilities. It becomes simpler when you think of the ISO setting simply as a means of getting the shutter speed you need. Here are some examples of what we mean.
At night on a tripod: ISO100
Always use a tripod for night shots when you can, because when you've got the camera locked in position you can use any shutter speed you like - and this means you don't have to increase the ISO and risk noise, even if your exposures run into many seconds.
Snapshots after dark: ISO1600
The latest DSLRs can get great shots even at really high ISOs, so it is perfectly possible to shoot handheld indoors and after dark. But you will need a fast enough shutter speed to avoid camera shake, so try ISO1600 to start with, or use the Auto ISO function.
Low light sport: ISO6400
The problem here is subject movement. Sports are fast moving and you'll need a fast shutter speed of 1/250 sec or 1/500 sec to have any chance of freezing the action. This means you may need a very high ISO indeed - but that's better than blurred pics.
Using Auto ISO
The main reason for increasing the ISO in dark conditions is to make sure you can shoot at a suitable shutter speed. At the same time, you'll want to shoot at the lowest ISO you can, in order to get the best possible picture quality.
This means you can end up doing complicated mental maths right at the time when you should be concentrating on your pictures. But there's no need, because your DSLR can do it for you!
The Auto ISO sensitivity option lets you set the minimum shutter speed you want the camera to use and the maximum ISO, then works out the best combination instantly as you shoot.
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