When you are focusing on a single point in a scene, a certain amount in front of and behind the point of focus will also appear sharp in the photograph. How much of the scene appears sharp depends on the depth of field, which is a crucial concept to understand, not only for landscape photography, but for all photography.
Put simply, depth of field is the distance from the nearest to the furthest point in a photograph that appears acceptably sharp, though this isn’t a constant distance for every photograph. This is because depth of field is based on the specific combination of focal length, camera-to-subject distance, and aperture setting, and each of these has an impact on how large or small the depth of field is.
The three factors affecting depth of field
- The focal length of the lens: wide-angle focal lengths produce a larger depth of eld than telephoto focal lengths.
- The distance from the camera to the point of focus (subject): the greater the distance, the larger the depth of field.
- The aperture setting that’s being used: smaller apertures produce a larger depth of field. This is the most important of the three factors listed here.
Arguably, for the majority of your landscape photographs you will want to make sure that as much of the scene appears in focus as is possible, which means you will look to maximise the depth of field. Thankfully this is fairly easy to achieve—especially with sweeping views—as it is likely that you will want to use a wide-angle focal length to fit as much in the frame as possible, while distant views are, by definition, at a distance. So all you really need to do is set a small aperture (say ƒ/22 or ƒ/32) and you will have done almost everything you can to make sure that all elements in the frame, from the closest to the most distant, appear sharp.
These are the three ideal settings, but you won’t always be able to achieve them. Sometimes a limited vantage point may determine the focal length you have to use to frame your shot, or there could be more subject-dependant considerations. Say, for example, you wanted to photograph a blossoming tree filling the frame with its colourful flowers. You could do this with a wide-angle focal length setting (to maximise the depth of field), but this would mean getting physically closer to the tree, which would reduce the camera-to-subject distance, and so the depth of field. Switching to a telephoto lens to enable moving away wouldn’t necessarily help, as the use of a longer focal length would reduce the depth of eld. In both cases, the only control that is guaranteed to affect the depth of field is the aperture.
Depth of field and image size
From much that is written about it, it is easy to believe that depth of field is a distinct zone in the image in which everything appears sharp, with everything outside it appearing blurred. But this isn’t the case. In any photograph, only one distance (the plane of focus) is in focus. Everything else exhibits a degree of softness—depth of field is simply the term used to refer to those areas that are acceptably sharp.
What is acceptable is, of course, subjective—what you may find acceptably in focus may appear out of focus to someone else. In addition, it also relates to the size at which the image is viewed: a picture will naturally appear sharper when viewed at a small size on a computer screen, but when enlarged to create an exhibition-sized print, slightly soft areas will appear even more out of focus. For this reason, depth of field should always be treated as a guide, rather than an absolute measurement.
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