Readers Questions

Hey Steve;  What is the big deal with Auto ISO?  I just read the new Canon 50D announcement and noticed it as a new feature, don’t all DSLRs have this feature?

Thank, Joe D.

Joe -  Thank you for the question and it comes at a good time with the recent announcement of the Canon 50D.  Traditionally “Automatic” modes in cameras would automatically adjust a single variable of the main shooting variables of shutter speed, aperture, and ISO.  An “automatic” camera in “aperture priority” mode would automatically adjust the shutter speed to match the user selected aperture, or a camera in “shutter priority” mode would automatically select the optimum aperture against the user selected shutter speed.  With the advent of DSLRs and with every camera having a CPU built in, we then had “P” modes or “Program” modes that would select the best combination of BOTH shutter speed and aperture for the desired scene.

Traditionalists lamented the loss of control and “dummy modes” and wouldn’t complain too much when they showed up on entry level consumer level DSLRs such as the Rebel series, but took great exception to their inclusion on the more professional level DSLRs.   This kept “Auto ISO” regulated to the point and shoot market. 

Recently Nikon started offering “Auto ISO” on their newest DSLRs separate from all the exposure modes save for the “P” modes where it was automatically included.  What does this mean?  Let’s take a sports photographer shooting a football game.  He’ll want to set his camera on “Shutter Priority” mode with say a minimum shutter speed of 1/500th of a second considering the speed of the players and that he’s probably using a 300mm lens or greater.  This means the DSLR will automatically select the appropriate aperture for the shutter speed for him.  Great, now he can concentrate on the action and taking pictures and not settings.  But what happens if the sun is setting and the player he’s capturing at 8fps (frames per second) runs from a sunlit area of the pitch to a shadowed area of the pitch and there’s not enough light for his selected shutter speed, ISO, because the aperture can only go so low?  What would happen is the camera would stop taking pictures and he’d miss the shot.  Now, say he starts at the sunlit side of the field at 1/500th, ISO 100, and as he follows the player the aperture is being adjusted F5, F8, F4, F2.8 maintaining proper exposure.  But now he hits the shadow area and F2.8 no longer provides enough light for proper exposure the ISO will automatically change to ISO 200, 400, or whatever is needed to maintain the desired/selected shutter speed of 1/500th.

Astute professionals have asked for an AUTO ISO feature for years, only to be drowned out by the traditionalists in the photography forums and marketing listened.  Recently Nikon saw the light and with the option available professionals and amateurs alike have discovered what a useful tool AUTO ISO really is.  Canon resisted, but with the 50D offers AUTO ISO for the first time.  Personally, I’m very glad to see it.  As long as we can still easily select the ISO manually, an AUTO ISO model only adds to the bucket full of tools the modern photographer has to draw from.

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