Tip: How to perfectly focus a self-portrait

Please excuse the poor quality model in this photograph but this is a tip about self-portraits so it's all I've got to work with.

It's a fact of life for photographers that we sometimes have to take pictures of ourselves. Often it's just for practice when we're learning a new lighting technique so it doesn't have to be a good photo, but secretly I think we all hope it will be, so we want it to be correctly focused. If all the planets fall into line and you somehow get that one photo of yourself looking like Tom Cruise then you want it to be sharp in the right places, and that means getting your eyes in focus.

If you use standard auto-focus then chances are the camera will focus on the end of your nose, more than a centimetre forward from your eyes. Sometimes it will focus on the bridge of your nose but that's still about half a centimetre forward from your eyes. It could possibly focus on your mouth but that's almost certainly going to be further forward or back than your eyes, depending on the angle of your head. What you can be sure the camera will not focus on is your eyes.

So how do you solve this problem?

There are two well-known but shoddy techniques that you can try:

• Use a small aperture for a large depth of field so your whole face will be in focus. But depth of field is an artistic choice so if you want a shallow DOF then you should use a shallow DOF. Using a deep DOF solves one problem by creating another. Bad idea.
• Trial and error. Auto-focus the camera then take a few photos, move forward a little and take some more, more forward again and take some more, maybe move back a bit and take some more, etc. But you know from doing portrait sessions with other people that you might take 100 frames to get the one you want, so what if your one good frame of yourself is one of the 90% that aren't properly focussed? Bad idea.

The solution is incredibly simple. It occurred to me when I was doing a self-portrait a couple of days ago for the latest Strobist lighting challenge. Before you scroll down, please take a moment to see if you can figure it out, otherwise you'll kick yourself when I tell you!

Here's a clue: Show the camera what you want it to focus on.

Before I tell you the secret, I'll prove that it works. Here's a close-up from the photo at the top of this post. It was taken at 70mm with the aperture set to f/3.5 so the usable depth of field was only a few millimetres. As you can see, though, my eye is perfectly sharp and my eyelashes are perfectly sharp, but my eyebrow and the bridge of my nose are out of focus. Perfect.

Okay so here's how you do it…

Although the portrait is brightly lit, the room was totally dark. The photo was lit by flash but the camera needed to focus in ambient light, which was non-existent — it could have hunted for focus all day and it would never have found it.

So I held a small torch next to my eye and then used a cable release to auto-focus the camera. The only thing visible in the room was the bulb of the torch and the part of my eye that it was illuminating, so that was what the camera focussed on. Then I moved the torch away and took the photo. Result!

The white background… uh, wait for it… that was a piece of foam board leaning on my back with one corner stuck down the back of my trousers to hold it up! How's that for an improvised background?!