Thursday, August 14, 2014
Back Button Focus
As promised, here is information on Back Button Focus (also called rear button focus).
In the old days before autofocus was invented, the shutter button had only two functions: press down partway to take a meter reading, and then press down fully to take the picture. Focus was not tied to the shutter release. To focus, you manually turned the focus ring on the lens.
But since the advent of autofocus, we now have 3 separate functions occurring on the shutter button. That was a poor decision on the part of camera manufacturers. By tying the focus function to the same button as tripping the shutter, it means that each and every time you press the shutter button, your camera attempts to re-focus. The net effect is that a series of images of the same subject can vary in focus even if neither you nor the subject has moved. Each time the lens has to hunt for focus, there is a good chance that it will not lock onto the precise area you want sharp.
But not to worry, there is an easy fix. Remove the focus function from the shutter button and put it someplace else. Most camera bodies allow you to do that by moving the focus to a button on the back of the camera body. This is still the same autofocus as always, you just press a different button than you did before. While you may balk at this at first, it is the best thing you can do for your photography of any subject, regardless of whether it is a stationary subject or a bird in flight. If you have a choice, set the focus function to the "AF-ON" button rather than other buttons that might also give you that option.
Most Owner's Manuals are notoriously bad at providing this information. For virtually all cameras, it is a Custom Function setting. For some cameras two separate functions have to be set in order to remove the focus from the shutter button AND move it to a back button. The best way to get the information clearly is either on YouTube or other sites that will come up during a google search. This is the YouTube link http://www.youtube.com/ Once on the site, type in your camera body in the search box near the top of the window. Here are a few links to get you started:
for Nikon - http://www.youtube.com/watch?v=gd2zk9FRjUE
for Canon 5D Mark III - http://www.youtube.com/watch?v=xqX1FO1XGFI&list=PL703F1832A905834A
for Canon 60D - http://www.youtube.com/watch?v=1F4KFyz7KoE&list=PL703F1832A905834A
Once you have moved the focus function to a button on the back of your camera, you will use your thumb to activate that button, and your index finger to use the shutter button as always. It might take a little time to get used to it, but it will make your life so much easier. For this shot of a church in Charleston, SC, I focused on the chandelier in the ceiling, using my thumb to activate the back button focus. Then I took a series of shots from the same position, and did not need to focus again. Once I knew the chandelier was sharp, I could take many exposures by activating the shutter button, knowing that the point of sharpest focus would not change because neither I nor the chandelier was moving.
Shutter Speed 1/100 sec. Aperture f/4. ISO 800. Lens: Canon 17-40mm f/4L, set at 29mm. Camera: Canon 5D Mark III. Handheld.
TODAY'S QUOTE: "Focus on your potential instead of your limitations." --Alan Loy McGinnis