Back-button Autofocus

Have you ever been completely over the moon about discovering something and tried to explain it to someone else, only to then have to explain why it’s “sooooo amazing!!”?

That was me last night trying to explain to my family how thrilled I was to discover back-button autofocus on my Canon 450D. I’d never heard of it before, I don’t know if that’s due to me missing something, or just that it’s not commonly known. But in my view it’s the greatest invention since… since the thing before they invented sliced bread.

The site I found for instructions is specific to Canon EOS. A quick search turned up some Nikon users discussing it, although I don’t know which models implement this. Here’s the link for Canon users.

I recommend reading through once quickly before trying to change anything as the article discusses back-button auto focus a lot, but doesn’t explain how to change any settings until near the very end. Also, the actual wording in your custom functions menu are likely to be different than the example ones on the site. You may understand it all straight away, or you may be like me and have to play with them until it makes sense and does what you want.

That’s great… but what is it? 

This is my cue to make a confession: I rarely use manual focus.

I’d love to have the confidence in my focusing skills but I tend to shoot fast, and often miss shots if I stop to mess with focusing. Like any photographer, I hate to miss out on photos because they’re badly focused. And modern auto-focus is often so quick and crisp that it seems a shame to waste it. Or maybe I’m just lazy and making excuses. Either way, I usually use auto-focus.

The problem with auto-focus is that I often find my camera’s focus drifting between the time I press the shutter button halfway to focus, and all the way to release the shutter. This is especially true when I try to lock focus on an object and re-compose the image before taking the photo. And if I have a stationary subject I still have to re-focus every time I take my finger off the shutter button. Well no more.

Back-button AF takes the focus control from the shutter button and puts it on a button on the back of the camera instead. Changing these settings has turned what was my AE lock button into a dedicated focus button, and I have set my half-pressed shutter button to be AE lock, so that feature is not only still available, but is far more accessible and useful to me now.

Once I’ve focused I can now recompose to my heart’s content, and take as many photos as I like without ever touching the focus. The Canon site gives a lots of examples of where this can be useful.

It takes some getting used to, but I love it already and doubt I’ll be going back to standard AF in a hurry. If you have a Canon SLR (or any other that has this function) give it a try and see if you like it!

Oh, and one last point. This function is only activated in the “creative zone” modes (P, Av, Tv & M), so if you click the dial to the “green box” auto mode, you can hand it over to anyone to use without having to explain how your focus works. Handy.


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