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Ever wondered what those vertical lines were on the rear edge your classic lens, or underneath the distance window on newer lenses? Here’s a guide to what they are, and how they can come in handy.

Those lines make up a “depth of field” (DoF) scale, a handy tool for figuring out just what in your picture is and isn’t in focus. If you’re using an SLR, you can use your DoF preview button to stop down the lens and get a rough idea of things - which is why many modern budget lenses omit these marks - but in this case, being able to see the end result isn’t quite as good as having the scale. Why?

Here we can see the DoF scale as the bottom set of numbers on the lens. Just above that is the distance scale [white numbers are meters, red numbers are feet], and then at the top is the aperture ring. The lens is focused to one meter, as indicated by the 1 aligned with the big dot, and the aperture is set to f/8.

Let’s say you’re taking a picture of your friend in front of a distant mountain range. You want to get both him and the stunning natural scenery behind him in focus. Since your friend is a meter away from you, you set the focus to one meter - but how can you be sure that the background is in focus too?

To see what’s in focus, we can check the DoF marks corresponding to our chosen aperture. Since we’re at f/8, the area between the two lines marked 8 indicates the area at acceptable sharpness; here, from about 0.65m to 2m. But we know that the background is far enough away to use infinity focus, and the infinity mark isn’t within the sharp area marked within the scales.

We could stop down to f/16 or f/22 to get everything in focus, as the DoF scale indicates. But what if you’re set on using f/8?

This is where “hyperfocal focusing” comes in. This technique allows you to get everything in focus past a certain distance. To set your lens to the hyperfocal distance, just align the infinity mark with the corresponding aperture mark. As you can see, the line from “f/8″ is pointing towards the one meter mark, and the infinity mark. Now, we get everything from just under a meter to infinity in focus at f/8, a far greater depth of field than with the previous setting, and enough to get both your friend and the mountains in focus.

This technique isn’t just useful for “getting it all in focus”, though. In fact, it’s one of the most basic tricks in the book for street photography - at the hyperfocal distance, you no longer need to stop to focus at every shot, allowing you to snap away immediately after framing, or even from your waist, since you’d be sure that everything from the acceptable distance to infinity will be sharp. All you have to do in that instance is to make sure your subject is past the one meter mark, or the acceptable distance you define, and it’ll be rendered sharp.

This post is tagged depth of field, dof, hyperfocal distance, photography tutorials