Back button Auto-focus

At the weekend I got lots of tips from Paul Ronan, a local photographer, including an intro to the possibilities of post processing (with RAW images), see some of the examples on my flickr stream

The biggest thing I took away from the day though was changing one setting on the camera which will change the way I shoot from now on. Here is an article that covers it well, going into detail for the 7D.

How and Why I Use the Back-Button AF

But basically on the 550D:

On the Canon T2i [550D], press “Menu” and navigate to custom function IV-9: “Shutter/AE lock button”. Your options will be:
  • 0: AF/AE lock
  • 1: AE lock/AF
  • 2: AF/AF lock, no AE lock
  • 3: AE/AF, no AE lock

That’s “Custom Functions” under the 3rd  yellow spanner symbol, then scroll across to #9.



Confusing to read initially, before the “/” is what the shutter does (half way down) and behind the “/” is what is controlled by the rear AE lock or star button. So 1: AE lock/AF meaning the shutter button now does auto exposure lock and the rear button now controls the auto focus.


The canon article goes into more detail on how and where to use Back-Button Auto Focus Explained

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