I use Av as 'default' mode and I think it is much more common. The reason is that once you have a shutter speed fast enough not to blur the shot it doesn't matter what it is, but aperture controls the depth of field so it's something that wants more careful control. Also, often with a zoom lens you may want to stop it down a bit to get the best quality..

Even when shooting moving targets and a fast shutter speed is the most important part of the exposure, I use Av: just leave the lens wide open and you'll get the fastest shutter speed possible for the light..

Best wishesMike..

Generally, Av is used when you want a set amount of dof in every shot. Tv is used when youn are constantly shooting movement or action and you know you want a faster enough shutter speed in all your shots to stop the movement..

If you are asking which mode is the best, there isn't any. which you use is determined by the scene and the photographer intent and desires...

One good reason to use Av, implied in the first reply, is to choose the aperture to suit the lens you're using. My Sigma 18-200 OS is sharpest at f8-f11. I leave it there for most shots unless I want something different..

Phillhttp://www.flickr.com/photos/philllister..

Tv means that once you set your shutter speeds, you are safe as far as getting sharp pictures goes, even in the sun goes behind a cloud. Depther of field will change, but at least your shutter speed will not drop while you are not paying attention, making your shot blurry for sure..

BAK..

Thank you all. I had read about them, but I was still somewhat confused. Thanks for your help.Debhttp://www.flickr.com/photos/20446885@N00/.

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BAK wrote:.

Tv means that once you set your shutter speeds, you are safe as faras getting sharp pictures goes, even in the sun goes behind a cloud.Depther of field will change, but at least your shutter speed willnot drop while you are not paying attention, making your shot blurryfor sure..

BAK.

Sort of.....but you may find yourself running out of apature and badly underexposed..

Apature is limited and pretty much stops at f1.2 (there actually are f1.0 and under lenses but almost noone can afford them). Time on the other hand is abundant and measured in years..

A member of the rabble in good standing...