Depth of Field - What it is and How to Control It
Depth of field (DOF) is the amount of your photograph that's acceptably sharp.
If you focus on a barn, a certain amount of the field in front of, and behind, the barn will also be in focus.
For example, it could be everything between 6 ft and 8 ft from the camera, or everything from 30 ft to infinity.
("Infinity" means "so far away that farther doesn't make any difference.
") The depth depends on three things: the distance between the subject and the lens; the focal length of the lens; and the aperture setting.
These days, most lenses don't, which is a shame, because they're very useful.
If you're trying to get the whole of a deep object in focus, for example the famous sign at Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch train station in Wales, you should focus a third of the way into it.
The hyperfocal distance For landscape photography, you naturally want distant objects like mountains to be sharp.
The obvious thing to do is to focus on infinity.
But that means that half your depth of field is "behind" infinity and wasted.
You want to focus so that the far edge of your depth of field is at infinity.
This point is so useful that it's got a special name -- the hyperfocal distance.
If you have a lens with the depth of field markings, it's easy.
You can just put the infinity symbol on the mark for your aperture.
Actually, you'll do better to focus on your foreground interest, note the distance, and find the aperture which gives a DOF from there to infinity.
If your lens doesn't have this, there are several DOF calculators online, some that run under windows or Mac, and and at least one iPhone app.
Since you might not have Internet access halfway up a mountain, I suggest you make a note of the hyperfocal distance at various focal lengths and apertures and keep it in your kit bag.
This may take practice, but once you master depth of field, you'll have full control over just how much of your photograph is sharp enough to draw the viewer's eye.
If you focus on a barn, a certain amount of the field in front of, and behind, the barn will also be in focus.
For example, it could be everything between 6 ft and 8 ft from the camera, or everything from 30 ft to infinity.
("Infinity" means "so far away that farther doesn't make any difference.
") The depth depends on three things: the distance between the subject and the lens; the focal length of the lens; and the aperture setting.
- The distance between the subject and the lens- The farther the subject is from the lens, the greater the depth of field.
It's, much easier to get a good depth of field in a landscape photograph than a macro shot.
Using my 50mm lens at f/16, I can get everything sharp from 8 ft (2.
4 m) to infinity, or from 16" (0.
4 m) to 18" (0.
46 m).
This makes focusing for a macro shot very difficult. - The aperture- The narrower the aperture, the greater the depth of field.
That same 50 mm lens at f/8 will get everything sharp from 16.
5 ft (5 m) to infinity.
At f/4, just 33 ft (10 m) to infinity.
So if you use a wide aperture and focus on the mountains, the foreground is out of focus.
This is why so many landscape photographers use small apertures.
Of course then you need a slower shutter speed to compensate, and you're likely to need a tripod. - The focal length of the lens- For the same camera-to-subject distance, a telephoto lens will have a shallower depth of field than a wide angle.
My 28 mm lens at f/ 16 will focus sharply from 10 ft to infinity, which gives as good a depth of field as the 50 mm lens at f/11.
That's a big help in low light.
On the other hand, a 200 mm lens, even at f/32, will only focus from 32 ft to infinity.
the best you can do by way of foreground will be colored blotches
These days, most lenses don't, which is a shame, because they're very useful.
If you're trying to get the whole of a deep object in focus, for example the famous sign at Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch train station in Wales, you should focus a third of the way into it.
The hyperfocal distance For landscape photography, you naturally want distant objects like mountains to be sharp.
The obvious thing to do is to focus on infinity.
But that means that half your depth of field is "behind" infinity and wasted.
You want to focus so that the far edge of your depth of field is at infinity.
This point is so useful that it's got a special name -- the hyperfocal distance.
If you have a lens with the depth of field markings, it's easy.
You can just put the infinity symbol on the mark for your aperture.
Actually, you'll do better to focus on your foreground interest, note the distance, and find the aperture which gives a DOF from there to infinity.
If your lens doesn't have this, there are several DOF calculators online, some that run under windows or Mac, and and at least one iPhone app.
Since you might not have Internet access halfway up a mountain, I suggest you make a note of the hyperfocal distance at various focal lengths and apertures and keep it in your kit bag.
This may take practice, but once you master depth of field, you'll have full control over just how much of your photograph is sharp enough to draw the viewer's eye.
