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12-23-2009, 04:41 AM   #1
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Using AF.C instead of AF.S for stills

A problem I have with AF.S is that the shutter won't release unless the target is locked, especially and if not, predominantly in low-light. Sometimes this results to certain lenses creeping in "micro-lengths" from left to right which doesn't affect IQ at all. This can sometimes slow down the shutter release time in milliseconds to even a second; although in milliseconds, the time can still be quite valuable. Since it's moving in "micro-lengths", it is already in-focus enough where there is no need to worry about out-of-focus. Not only does this help reduce the problem of creeping and not being able to snap the picture at the perfect moment, it also reduces the annoyance of loud screw-drive lenses creeping.

If I use AF.C for still shots, this allows me to release the shutter at any given time I want. All I need to do is press the shutter button half-way to in-focus, then pull it all the way down without having to wait for the creep to end.

Now this is the question, will this affect the quality of my images in any way at all if I were to use AF.C instead of AF.S to shoot stills, even if my timing to release the shutter in AF.C is equivalent to when the creep ends in AF.S? Hope you guys get what I'm trying to say, it's kind of difficult to explain but I tried my best. Also sorry if this sounded like a stupid question, but I'm only asking because there are AF.S mode which is specifically designed for stills while AF.C is designed for continual motion. I thought maybe somehow IQ would play a part in using AF.C for stills when AF.S is designed for stills.

Last edited by LeDave; 12-23-2009 at 04:47 AM.
12-23-2009, 05:45 AM   #2
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It all depends upon your chosen lens opening. At f:1.4, it will make a difference. At f:11, it will look perfect.
12-23-2009, 06:31 AM   #3
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As the previous poster pointed out, your shots are likely to be out of focus, but whether you will notice will depend on the depth of field ie aperture youare using.

I would stick to AF S for still shots.
12-23-2009, 07:22 AM   #4
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I only use AF-C cos I have far more control and can act much quicker. Now I have not tried this on Pentax, but I have found my 40D is more sensitive in dim environment with AF-S than with AF-C. Still, I use AF-C almost exclusively.

12-23-2009, 12:54 PM   #5
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I use AF-C for sports shots. If at all possible I try to shoot at f8-f11 and it really doesn't matter unless the camera picks up on something way off in the background but that will be visible in the viewfinder. It's really going to depend on the aperture and the lens you are using along with the distance away from the subject. Obviously, when shooting a still subject or a landscape, there is no need to rush and it would always be best to make sure your focus is right on. It's frustrating to loose a shot when the shutter won't fire in AF-S because the focus may have been slightly off but well within the DOF at that aperture. Try shooting in both and compare the results.

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