Back-button auto focus is a very useful technique in certain situations and is explained in plain English here (read from the beginning to the part about waiting for your subject to do something interesting). Basically back-button AF takes control of auto focus away from the shutter button and gives it to a button on the back of the camera.
The method described here has been tested on a Panasonic Lumix DMC-G2 and I’m almost certain that it will also work on the G1, GF1, GH1, and GH2. If you try this method on one of these cameras please post a comment and share the results.
Step 1: settings
- AFS or AFC
- AF/AE Lock set to AF*
- AF/AE Lock Hold set to On*
Items marked * are in the Custom section of the menu.
Changing these settings in the middle of a shoot slows things down so I store them in one of the custom memories.
Step 2: shooting
One you’ve made the above changes or entered your custom mode put your AF frame over Subject A and press the AF/AE Lock button. ‘AFL’ will appear in the viewfinder and focus is now locked on Subject A until you press the AF/AE Lock button again. A half press on the shutter button will lock the exposure setting while you hold the button down (even though ‘AEL’ does not appear in the viewfinder), so the back button controls AF and the front button controls exposure.
To change the focus to Subject B place the AF frame over him and press the AF/AE Lock button twice.
When you see ‘AFL’ in the viewfinder you’re in back-button AF mode, and when you see ‘AFS’ or ‘AFC’ the shutter button is controlling both focus and exposure.
Doing it is a lot easier than reading about it.
This undocumented feature is part of the reason why, apart from the GF2, the Panasonic G series has been quite successful at serving both point-and-shoot people and advanced photographers. Some firmware changes would make the G2 even better for the latter group.
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