focusing..

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lazaroonie

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Patrick
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been thinking a lot about focusing recently. what I am trying to sort out in my head is under what circumstances you would use autofocus, and manual focus.

all things being equal, and for example using a good canon lens on a canon body, is it true to say that provided you are focusing on the right subject, then the autofocus mechanism will generally result in a sharper picture, based on the simple presumption that your eyes are generally not 20:20.

I can see times where you would want to manually focus, but in general is it not better to use either full auto or auto focus with manually defined AF points ?
 
It really depends on your gear and environment.

For example, in bad light, the AF system can easily go hunting for a while and end up not focussing at all. The Canon USM lenses focus a lot quicker and more reliably in pretty much all circumstances than non-USM lenses. If you're shooting with a huge aperture and hence almost zero depth of field, even the slightest mis-focus will be glaringly obvious.

Personally, I try to use AF whenever I can. I'll select an AF point myself, have the camera focus, reel off a few shots and review them on the LCD screen at 100%. If I see the camera is mis-focussing, I might tweak the focus a bit myself after letting AF get close enough for rock & roll. The viewfinder on the Digital Rebels can often be too small for manual focus so I switch to live-view (on my 450d - don't think the 400 has it) if needs be.

Shooting fast moving subjects in low light with a wide aperture is difficult at best so I'll let the AF system do its work there 99% of the time even though there's a high chance some of them are out of focus slightly. Call it artistic licence!

Are there any occasions where you haven't been satisfied with the results of auto-focus?

George.
 
I almost exclusively use AF, the only real exception being macro photography where it is much harder to get the focus precisely where I want it.
Most viewfinders modern viewfinders are designed for AF function and not to assist manual focus. If you intend on doing a lot of manual focus some SLR's have replacable viewfinder screens that offer a split image that you then align to get focus. This, i'm told, is much simpler.
 
The only times I use manual....
is for taking panoramas ( the focus needs to be fixed or at least under control)
For macro close up work when it is easier to move the camera than change focus.
Thirdly for fast action when it is an advantage to prefocus on a spot and wait for the subject to hit it.
 
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