Teachable Moment - Auto ISO in DSLR Photography

As a rule of thumb it’s good to keep your ISO as low as you can. This is no problem in landscape photography because, typically, you’re working on a tripod. With subjects like wildlife, sport and young children, however, ISO is a very active variable. While it is possible to manually adjust the ISO as you go, I find that using Auto ISO really helps me just to get on with things.

When using a telephoto lens, as we tend to do with wildlife and sport, shutter speed becomes paramount. The longer the lens, the more it emphasises any camera shake (movement introduced to the camera by your hands or by the camera mechanism) so your shutter speed has to get faster and faster as your focal length gets longer and longer. It’s important to at least match your shutter speed to the focal length of the lens - for example, 1/200th of a second for a 200mm lens, 1/400th of a second for a 400mm lens and so on - to eliminate the effects of camera shake.

What does any of this have to do with ISO? In Auto ISO you can lock-in a minimum shutter speed (to match the focal length of your lens) which the camera can’t go below. The camera will automatically select the lowest ISO which allows the minimum shutter speed to be maintained and the ISO will increase automatically when needed.

If you use the camera in Aperture Priority, you can tell the camera the f/ stop you want (controlling your Depth of Field), lock in the minimum shutter speed in the Auto ISO menu (to match the focal length of your lens) and let the ISO automatically adapt in the background to support these settings.

Shooting in this way frees up my brain-space and allows me to just get on with my photography, concentrating on what I’m looking at - the scene, the subject, the light and the composition - without being distracted by having to move dials and press buttons when the action starts.

As always, it’s about making the equipment up to work for you and not against you.

Good subjects for AUTO ISO:

  • Any time you use a long / telephoto lens

  • Wildlife

  • Weddings / Event coverage

  • Kids / Family

Do you use Auto ISO or have you never tried it? Let me know what you think in the comments and please share this if you found it helpful.