JacaRanda said:
Okay, let's take this fellow's first instance of why one would want to use BBF.
"
EXAMPLE NUMBER ONE
First, suppose you are shooting
portraits. The person who you are shooting is standing still and you want to take several different shots of the person. You take your first shot, and then change your composition and need to move your focus point to be on the person’s eye. If your camera has 40+ focus points like many DSLRs do, you have to use the four-way selector to tediously move the focus point to the correct spot, focus, and then take the photo. How annoying!
You can use back button focusing to solve this problem because the distance between the photographer and the subject stays the same between both shots, but the composition changes. With back button focusing,
the photographer activates focus for the first shot, and then is able to recompose infinite times as long as the distance between the camera and the subject remains exactly the same.
You’ll note that there are other ways to solve this problem, such as
focus and recompose (equally tedious, but sometimes it’s your best bet), or holding the AF-L, AE-L button, but that is just plain annoying. Back button focusing is superior in this instance as long as the photographer is
careful not to change the distance between the camera and the subject (which would throw off the focus) when using shallow depth-of-field."
******
A great example of THEORY clashing horrifically with the actual practice of portrait or model or lifestyle photography.
1) Here's a steel-tape FACT. Focal plane at 90.25 inches to X of gaffer tape on wall. Twenty-five degrees to left of the lens-to-target axis, the measured wall-to-focal plane is 97.00 inches distant. That is a 6.75 inch distance disparity. More than the depth of field will cover at wide aperture. Focus and recompose with a 35mm lens will throw the focus off by almost seven inches. The author of this piece suggests that instead of taking .25 seconds to use the jog wheel on the back of your camera, to just skip placing the AF point properly, and instead using using focus and recompose! Wow...how newbish.
And the wording: "
recompose infinite times as long as the distance between the camera and the subject remains exactly the same". I wish the world were that simple and perfect.
2) Steel tape fact #2: I set up a tripod with the camera plate a measured 47 inches from the floor. With the camera framed in "tall" mode, the center of the frame was a measured 91.25 inches to the wall. The distance to the ground wall/floor joint, at the ground? 103.25 inches. That means an 11.75 inch focus discrepancy. Very dicey. At wider apertures, this one is a loser.
The guy who wrote the piece above is not a very experienced photographer. But he did figure out how BBF works. And he wrote a nice excited piece about it, but his portraiture technique and knowledge utterly sucks.
He's basically saying, WTF, lock the focus somewhere between 7 inches and a foot off, and fire away. Uhhhh...no. Never. Ever. Photo technique articles that use faulty examples spread misinformation. And that is exactly why so many noobs shoot portrait sessions with EVERY FRAME out of focus, even at 15 feet, with their 35mm and 50mm lenses, even when they had stopped down to f/2.8. Bad advice from people who try to teach stuff they really have no business "teaching". Focus and recompose is a HORRIBLE method if one is so,so lazy as to use the center AF point, then to let go of the button and just blaze away? Just so,so,so wrong on multiple levels.
