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In some occasions autofocus doesn't focus what I intend it to. What is the better option - to use autofocus, focus what I want and recompose, or use manual focus in that situation?

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I'd say this is more a matter of personal choice most often. Sometimes you have to focus manually, or risk going nuts, simply because there is too much clutter in the image, throwing off the autofocus mechanism. Shooting macro images used to make me nuts that way. Remember, autofocus is a convenience, but you're the boss of the camera and you can tell it what to do. –  Greg Apr 1 '11 at 5:30

4 Answers 4

up vote 7 down vote accepted

In general, modern AF cameras have focusing screens optimized for bright viewing rather than accurate focusing. This means that the AF system is potentially more accurate than your eyes using the focusing screen, if the AF system is calibrated correctly.

I've found that the wider the lens is, the harder it is to achieve critical focus while focusing manually.

For critical manual focusing, either use Live view, if you have it, or install a custom focusing screen for your camera.

If you are using AF and recompose, I've found it useful to decouple the focusing action from the shutter release. Most cameras will let you assign focusing to a separate button, instead of having to maintain a half-press of the shutter while recomposing-

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I tried the decoupling technique for some time, but fell back to the normal operation. I guess old habits are hard to change. I wonder, though, why do you find it more useful, except if there is usually a long lag between you focusing and taking the shot? –  ysap Mar 31 '11 at 23:44
    
Sports Illustrated recommends their photographers split the functions and even have settings on siphoto.com to that point. Part of the advantage is it allows autofocus separately from locking the exposure settings, giving you greater control. When shooting action sports I found it convenient because I could track the action, I'd see someone or something would get in the way, and, instead of having the camera try to adjust its focus to the intervening object, I'd temporarily release focus, then push it again when clear. Splitting also works nicely for nature/landscape/macro work too. –  Greg Apr 1 '11 at 5:36
    
ysap: I heard about it on some podcast and it just felt right after trying it. I'm raised on MF (Olympus OM was my first SLR) so focusing with one motion and tripping the shutter with another just feels right. When shooting portraits I usually try to get focus and then recompose or wait for the expression I want. –  gerikson Apr 1 '11 at 9:29

Focus and recompose will work just as well in most cases; the exception is when the aperture is so wide that the object being focused on actually leaves the plane of focus when you recompose (most likely in macro photography). If you are able to select AF points manually, then choose the one that's closest to the item you are focussing on to minimise this effect.

If you have the time and the means (e.g. zooming in on live view), manual focus will give you full control, but if you're in a hurry, stop down a few stops (if you can) and use focus and recompose.

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It's not just at macro distances - I've shot full length portraits with a 50 f/1.4 where the recompose was enough to cause significant focus errors! –  Matt Grum Mar 31 '11 at 11:01
    
Indoors at night, my Canon T1i/50 f/1.8 drops to f/1.8 immediately if I let it, and at times this means I can't focus-and-recompose. –  khedron Oct 28 '11 at 3:59

You don't state what camera model you're using but if it somehow happens to be a Hasselblad H4D series then you're in luck as your camera has a truefocus feautre.

This is essentially an orientation sensor so that you can focus and recompose and the camera automatically adjusts the plane of focus to accommodate for the shift when you recompose.

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It's only a Canon T1i :) –  eagerMoose Mar 31 '11 at 11:12

I always lock the auto focus point selection to the center and not auto point selection. That way I can first put the focus where I want and then recompose.

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You might get more exact focus by choosing the closest point instead. –  Imre Oct 26 '11 at 21:07

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