Something I've noticed folks with DSLRs do is aim off-center and then quickly bring the lens to the target. What's the point of this? What settings are they messing with? My best guesses are something to do with either white balance or focus. I don't know why I think this, just all I could think they might be doing.
I've been a pro photographer for about 18 yrs and I rarely do that for focus. I do that a lot for quick spot-metering in natural light though when I can't use my handheld meter for whatever reason.
On most SLRs, you have an optional spot meter, (which, for noobs is) a meter which only reads the reflected light in a small area in the middle of the frame. This lends killer accuracy in many situations vs the usual full frame or matrix metering, which is often wildly inaccurate, especially in high-contrast scenes, or scenes with a lot of harsh, close (especially in-frame) backlighting. Often this spot meter function is assigned to a button on the camera that must be depressed to activate. (It's been a while since I've had to set up a new camera, but on Canons, IIRC, you can configure this in the custom functions setting.)
The spot meter is the way all old SLRs and most medium cormat cameras with in-camera meters used to operate. When more modern SLRs made full frame or matrix metering the vogue, a lot of photographers never became familiar with spot metering, which is a real shame, cause it's a powerful arrow to have in your quiver.
To use it properly though, you must remember that a spot meter is a reflective meter, meaning that, like all reflective point meters, it always wants to give you a reading to make whatever you are metering the shade of approx. an 18% grey card. Now, obviously it's a rare occasion when you'll have one of those in the scene you're shooting, so, if you can meter off something that approximately that density, (like say a pair of half-faded blue jeans) you'll get a good result. If you want to get good at this, carry a little piece of an 18% gray card around with you and just walk around comparing it to stuff you see in your everyday life often. Try to ignore the color, and just consider the shade the material reflects. You'll get pretty good at spotting things to spot meter from in no time if you really want to learn and make a simple effort.
Similarly, when you get good, you could meter off something you know is too dark or too light, and adjust your exposure accordingly a few stops up or down in the correct direction, once you get practiced at using the meter.
When I autofocus with a normal SLR with the various multiple points, I hardly ever do what you describe, as I'm pretty adept at switching between the closest points on the fly (well, in the canon system anyway) but I do that action a lot for spot metering, because I use the spot meter A LOT in situations that require it.
I hope this long explanation made sense.
) since there is big storm tomorrow in the east.
