By default, most DSLR (and all point and shoot) have the focus and shutter assigned to the same camera button. This is how most people learn to shoot: half-press the button to focus then press completely to take the picture.

While a lot of people use this configuration, many pros prefer to separate these features on two buttons for the following reasons (it is also called “back button focus”):

  • Once the focus is set, there are no risks of accidentally changing the focus point when taking taking another shoot.
  • Pictures can be taken faster since the camera does not have to wonder if it should focus or not, it simply take the picture.
  • When shooting in AI Servo mode, you can keep the camera focusing while taking picture, ensuring better focus.

It takes a bit of time to get used to it (1-3 days) but it is worth it, you will quickly wonder how you ever managed to shoot the old way.

Some additional reading:

Canon EOS 5D Mark III – Tutorial Back Button AF:

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chief astronomer at planet5D LLC
Mitch "planetMitch" Aunger is the creator and mastermind behind — which covers every aspect of HDSLR cameras (and a whole lot of other cameras as well). A lover of photography since his early days, he graduated to selling stock photos to make a little bit of spare cash. It wasn’t much, but it allowed him to upgrade to better cameras as well as computers, and it wasn’t taking money away from feeding his family.
He loves the stories that the still image can tell. In the summer of 2008, he read a story written by Arnold Kim called “I Quit My Job” — Arn is the owner of He started macrumors in 2000 as a hobby, and by 2008 he was making more money with the site than he was on his day job, so he quit. The surprise to the story is that he was a doctor making more than six figures! Right then and there, planetMitch dreamed about doing the same thing.
September 2008 rolled around, and Canon announced this new version of the incredible 5D — the Canon EOS 5D Mark II. It was the first Canon DSLR to shoot full HD video and the earth moved! (It really was a huge deal in the photography world.) planetMitch knew if there was ever a chance to ride a wave of something he was really passionate about, this was it — and the blog at was born. It is now one of the most popular HDSLR blogs on the planet, and he is making a full-time living from blogging. He couldn’t be happier!
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