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 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 is Canon specific, with instructions for Canon EOS models, but I did a search earlier and found people talking about it on some Nikon threads also, although I don’t know which models implement it (apart from the D90, which I know uses it). Here’s the link for Canon users.

I recommend reading through quickly first. It doesn’t explain how to change any settings until the end and frustrated me trying to work it out as I went through it the first time. Also, the actual wording in your custom functions menu will likely 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 shoot quickly, and often miss shots if I stop to mess with focusing. I hate to miss out on photos because they’re badly focused. Or maybe I’m just lazy and making excuses. Either way, I usually use auto-focus.

The problem 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.

Back-button AF basically 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. Once I’ve focused I can 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.