Back Button Focusing (BBF).
(BBF) is a technique of focusing a camera and maintain that focus. I got the idea from a comment that Chris82 made in his post immediately above. A quick Google shows that lot’s of Canikon users are trying to get their cameras to do it. Apparently, Many photogs use this technique for sports, portrait and landscape shooting. Try it and we can discuss the pros and cons. Many on the internet say they love it and would not go back.
Sony a7, a7R, a7S, a7II, a7RII or a7SII cameras can be reset to Back-Button AF, and focusing is then performed by pressing the AEL button. This probably will also work with all Sony 7 to 9 series cameras, A or E mount. Lower series cameras may not, I don’t have one to check. The steps for the A7 series are shown below, I have not tried the others yet. (A700, A77. A850/900 and A99.)
1. Press Menu> Cog 6 > Custom Key Settings > AEL Button > AF On.
2. Menu > Cog 6 > Custom Key Settings > AF/MF Button > AF/MF Ctrl Toggle.
3. Menu > Cog 3 > AF w/shutter > Off.
4. Come out of Menu. Turn the camera off and on.
Now, pressing the shutter release half way will not AF, you must now press the AEL button on the back to focus by using your thumb. When you see the camera focus, press the AEL button and the camera will automatically show the peaking, confirming perfect focus. The shutter button now only wakes up the camera on half press and fires the shutter on full press.
5. To come out of BBF you need only turn ‘AF w/shutter’ back On, leave the others settings as is.