January 22, 2009

PHOTO Q&A – Auto ISO

Brendan Coles (www.brendansphotogallery.com) wrote:

I was wondering what your opinion is regarding Auto ISO. Do you recommend manually setting your ISO or just leaving the camera on Auto ISO and let the camera decide which ISO to use?

Hi Brendan, if you’re talking about most point and shoot, and consumer level DSLR’s the answer is – I suggest that you manually set your ISO. Think of ISO as a third exposure control. You have shutter speed, aperture and ISO – all working together to help you get the right ISO.

Most cameras provide the best photo quality at a low ISO. If you get into a situation where the Auto ISO thinks it’s too dark, rather than open up the aperture, the Auto ISO may decide to crank up the ISO – inducing noise.

I could give other examples, but you should get the point. If you seek to be anything more than a snapshooter, learning how to properly set the ISO is a good idea.

There are a few exceptions to this rule. Owners of the new Canon 5 MK II, Nikon D3 and D700, as well as a few other high-end models have access to a different kind of Auto ISO. This more sophisticated ISO allows the photographer to set a constant shutter speed and aperture and then adjusts the ISO to match. This is very valuable, and I hope this feature finds its way to low end cameras soon. I wrote about this as one of the reasons I like the D3 in a post you can find in our TWIPPHOTO.COM archive. Here’s the salient passage in that post…

“Here’s a typical scenario for me. I photograph lots of flying birds. They don’t always cooperate with the light. I might start shooting a bird in direct sunlight, only to have it fly out of the light into shadow, and then back into the light. The result might be a four or five stop difference in light on the subject. It’s impossible to change the ISO on the fly, while trying to capture the bird in flight and in focus. But using Nikon’s Auto ISO, I just set my shutter speed to 1/1000th of a second and my aperture at f/5.6 then the auto ISO adjusts automatically for the lighting condition.”

I hope this answers your question. While I can’t answer everyone’s question on the blog, I still welcome them. They help me formulate an opinion about the things I cover here. And who knows, I might just pick your question to post for the world to see. Send them to [email protected]

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This post sponsored by the Digital SLR Store