Selecting Focusing Points

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Swamp Sparrow
(hand-held with AF, selected center focusing point)
As far a focusing points go, the general rule is "the more the merrier."  And of course, there's good reason why.  The more focusing points your camera has, the more your camera can choose from to make sure you get your subject in focus.  However, your camera can't think for you.  It doesn't know what you want in and out of focus, and so there are some situations where the camera simply cannot decide on the focusing points you want.  If you've taken enough photos, you've seen it happen.  The camera focused on the leaf in front of the butterfly or on the grass behind your daughter blowing the seeds off a dandelion.

Your camera will show you what focusing points it has chosen before you take the picture.  On my camera, the focusing points light up in the viewfinder, so I can check to make sure the camera is focusing on what I want.  Checking your focus before shooting is a good habit to develop, and in time it will become second nature.

But thankfully, your camera will also let you choose one focusing point (or a cluster of focusing points).  Check your camera manual to find out how to do this on your camera.  This allows you to take control of how the camera auto-focuses so that you can be careful to get what you want in focus.  I do this frequently, though I do it differently depending on whether or not I'm using a tripod.
  1. Hand-Holding: When hand-holding, I will often select the center focusing point only (or center cluster). When shooting, I center my subject, press the shutter down half-way until it focuses on my subject, then I recompose and shoot.  In the above photo of the Swamp Sparrow, I doubt I would ever have gotten the bird in focus if I relied on the camera to choose an autofocus (AF) point.
  2. Tripod: When using a tripod, I compose my photograph the way I want first, and then I select the focusing point that is covering my subject (or another object that is the same distance from the camera).  In the photograph below, I wanted the whole frame basically in focus, so I selected a focus point and an f/stop (f/16) that would let me get the whole scene sharp.
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Patapsco State Park, Avalon Area
(tripod, selected AF point covering the cascade)
If you have a consumer grade camera, your focusing points will likely be bunched around the center of the frame, and you may your subject may be outside of the focusing points you can choose.  In this case, the tripod technique won't work.  There is a workaround, though.  Loosen the ball head on your camera, center your subject, and focus on it.  Then switch your lens to manual focus (MF) , recompose, tighten your ball head, and shoot.  This will work for stationary subjects, but remember to switch back to autofocus (AF)  when you're done.

Your camera may have an AF lock that will let you temporarily freeze your AF while you recompose and shoot without switching to manual focus.  Personally, I prefer to switch to MF so I can take my time after focusing to get the composition, exposure, etc. that I want.