Hyperfocal Focusing with Digital: Because There's Not Much to See Beyond Infinity
When attempting to photograph a sweeping vista it's easy to focus the camera at the far horizon, stop the lens way down, and fire away. It might not be obvious, but there's a better way — a much better way, especially in the age of digital photography.
A camera lens is only ever focuses at one particular distance at a time. There's no way to actually focus on a range of distances. But when something is close enough to being in focus, we can't tell that it isn't. As such, distances just in front of and just behind the actual focus distance will be nearly in focus, so close in fact that we can't tell they aren't. As you probably already know, this "nearly in focus" range is commonly referred to as the "depth of field."
Exactly how near the actual focus point something needs to be to appear in focus depends on a number of factors. Most photographers know that aperture (f/stop) has a huge bearing on depth of field, but there are others including subject distance, sensor size and the infamous circle of confusion. At normal subject distances, available depth of field is split with roughly one third in front of the focus point, and two thirds behind. As subject magnification increases and you enter the world of ultra-macro, the split approaches fifty-fifty, but there's always a portion of this range in front of and behind where the lens is focused.
But leaving all these factors aside, there will always be a portion of the depth of field behind the focus point, so a lens focused at the horizon wastes all potential depth of field beyond that point. The farthest possible point of focus it technically known as infinity focus, but to me that only serves to confuse the point. I mean, how far away is infinity? But call it the horizon or call it infinity, it doesn't matter. Even though it seems impossible, a lens focused at infinity technically has some of its depth of field beyond infinity. Except in science fiction fare, there's nothing beyond infinity. So it makes no sense to waste part of your depth of field on something that can't really be there.
Instead, the trick is to set the focus distance such that the farthest point of what appears to be within your depth of field lies at the horizon. Thus, while anything that was beyond infinity would thereby be out of focus, as much as possible within the real world will appear in focus. A lens focused at this distance is said to be focused on the hyperfocal distance.
There are many ways of achieving hyperfocal distance. The actual math is far too complicated to do in your head. Prime lenses (non-zoom lenses) often have markings on their barrel to help you focus at the correct distance based on aperture. There are countless charts and calculator programs available both online and as Android and iPhone applications to do the math for you. I even have a t-shirt from a few years back created by Nikonians with a hyperfocal chart emblazoned on the front. In essence, all these methods boil down to the same thing. A lens focused at infinity with have its closest apparent in-focus point at the hyperfocal distance.
In practice, understanding this relationship used to be of little use in the field since there was no way effectively judge focus with film until you got the results back. Most digital cameras though allow you to zoom in on the LCD review image all the way to one-to-one if you need to. When you do, you can readily tell what looks in focus and what doesn't.
So first, go ahead and focus at infinity and take a test shot. It's then a simple matter of zooming in on the results, looking around and refocusing to the closest point that you judge to have acceptable focus. You can then shoot with confidence having found the desired hyperfocal distance on location with just your regular camera gear, and no complicated math or calculation aids.
When doing so, keep in mind the resolution of your camera's sensor relative to how large you present your work. Shooters using a new extreme resolution twenty-something megapixel camera who rarely ever uses their images for more than web images will clearly not need to zoom in as far as someone still shooting with a six to ten megapixel camera who is trying to make every pixel count in the final image. This is something you'll need to figure out based on your own needs and capabilities. Once you do though, you should be good to go.
Not all landscape photography is the same, but it's a common strategy to attempt to maximize depth of field. Ansel Adams did it, so it must be a good thing. Hyperfocal focusing is just one more case where digital gives you a way to solve an age old photographic problem in a way Ansel never dreamed of.