Don’t focus on the horizon if you want all of your scene to look sharp.
Whenever you focus your camera on something, there’ll be stuff in front and behind your subject coming out sharp too. That region where things look sharp will extend twice as far behind what you’re focusing on as it does in front. Or to say it another way, the thing you focus on will be about a third of the way into that area where things look nice and sharp.
That sounded awful when I wrote it, so hopefully it will make more sense in a picture.
You’ll see that the camera is focusing on a point within a line of posts, and while only one post looks sharp in front of that point, two posts look sharp beyond it.
So that’s why you focus a third of the way into the area that you want to look sharp.
To better illustrate these concepts I simulated what would happen if you used a very big aperture (very small f-number). Because as you’d know if you’d read my getting started article, depth of field gets smaller with the big apertures.
Because a common mistake people make when they want to get everything in focus — for example everything looking sharp all the way to the horizon — is to focus their camera on the horizon. But you’ll now realise that’s wasting most of the focusing potential of a camera, because two thirds of what’s in focus will be beyond the horizon! The best thing you can hope for then is that the horizon will be nice and sharp, but things in the immediate foreground will look fuzzy.
So what you want to do in those circumstances is to focus one third of the distance into the region where you want things to look sharp.
Yep, just like with so much other stuff, photographers have a fancy name for that distance. They call it the hyperfocal distance.
The next graphic (above) shows it happening again. The same rules apply: twice as many posts look okay beyond what the camera’s focusing on compared with the number in front. But depth of field is greater, so you get more posts overall looking sharp.
So in a landscape where you want everything to look sharp all the way to the horizon, you focus on something that’s one third of the distance to the horizon. And you’d be using an aperture appropriate for a big depth of field (in other words, a big f-number).
Now, if you’re using a wide-angle lens, then something like f/11 should be fine. If you’re not using a wide angle lens then you just won’t be able to get as much depth of field.