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Brewhaha
12-20-2008, 09:24 AM
I believe that I understand what it basically does: overexpose dark scenes and underexpose bright scenes. However, I am wondering if it does this by changing shutter speed one stop or aperture one stop? Or maybe neither?

Couldn't I just compensate for the exposure myself by opening or closing one (SS or Ap) of these one stop?

Joe Gardner
12-20-2008, 09:31 AM
You can do it both ways. :)

R
12-20-2008, 01:11 PM
The exposure compensation control (ring, button, menu item, whatever) makes your exposure lighter or darker regardless of the exposure mode your are using (except manual.) In P (for Program mode), it will change a combination of aperture and shutter speed (and ISO on some models) to adjust exposure. In A (for Aperture Priority - Canon calls it Av), you pick the aperture and the camera will adjust the shutter speed, including adjusting it for the amount of compensation you have selected. In S (for Shutter priority - Canon calls this mode Tv), you pick the shutter speed and it picks the aperture. In manual exposure mode, exposure compensation doesn't effect the exposure except for the "match needle" display in the viewfinder, so don't expect it to make any difference. (Note that some cameras will still try to adjust exposure in manual mode if you have "Auto ISO" enabled.)

Brewhaha
12-20-2008, 01:48 PM
So do you guys, Richard and Joe and whoever else, shoot in Auto ISO or do you manually set it each time?

R
12-20-2008, 06:33 PM
So do you guys, Richard and Joe and whoever else, shoot in Auto ISO or do you manually set it each time?

Since most of what I shoot (news, sports and magazine) requires me to live on the margins, such as trading high-ISO noise for a better shutter speed for example, I always set ISO myself, and I keep my cameras set so I can adjust it 1/3 of a stop at a time, as in ISO 200, 250, 320, 400... etc. When I am hiking and shooting the beauty of the southwest, on the other hand, I almost always "bottom-out" my ISO so my images will have the least noise, which equals cleaner large-sized prints. My wife, who is not as technically savvy or experienced as I am, tends to leave auto-ISO turned on, simply so she doesn't have to mess with it.

Keep in mind, though, that most of the modern DSLRs today have very acceptable noise at fairly high ISOs. Don't miss a shot because your ISO is too low and the image is blurred. And noise can be cleaned up in post-production, whereas if you miss a shot, it's gone forever.

http://myweb.cableone.net/abbysm/pix/AbbyCanyondeChelley02.jpg
Abby at Canyon de Chelley, October 2004

bryan
12-23-2008, 06:09 AM
With my Nikon D40, I find that Auto ISO works really well. ISO1600 can be noisy, but Auto ISO will only choose that in low light where hand holding at a lower ISO would be really hard. One time to turn off Auto ISO is when you're using a tripod, because then you're not worried about camera shake.

JP
12-24-2008, 05:41 AM
I have no choice but to select the ISO :haha: