Common questions about shallow and deep depth of field (6-10)
What are these other factors?
The two most significant factors are the focal length and the focused distance. The wider the angle of view of the lens, and the shorter the corresponding focal length, the more depth of field you get.
A wide-angle lens setting, therefore, gives you more depth of field than a telephoto one. The subject distance (or more accurately, the distance the lens is focused at) also has its role; the closer the focused distance, the less depth of field you get.
Is depth of field spread evenly in front of and behind the point you are focused on?
Almost never. In most normal situations, depth of field extends further behind the plane of focus than in front of it. Often the difference will be dramatic.
When shooting with a wide-angle lens and a small aperture, there will typically be a metre of depth of field your side of the focused point, but everything behind as far as the eye can see will also be sharp.
What about photographing macro subjects?
Depth of field at very close distances is evenly spread in front of and behind the focus point (but perhaps just a millimetre or two in each direction).
So what do I have to do to maximise my area of focus for deep depth of field?
First, set a narrow aperture (such as f/22). It may be necessary to use a tripod, or to increase the ISO to make small apertures feasible in anything but bright light.
Next, use the widest lens you can get away with for the subject, and stand as far away as possible. Finally, focus on a point about a third of the way up the frame to ensure as much of the shot as possible is sharp.
And what do I have to do to minimise depth of field and to maximise blur?
Use the longest lens you can get away with, and/or get as close to the subject as possible. Now set the maximum aperture available on your lens.
‘Fast’ lenses with wider-than-average maximum apertures are much better at this effect. Cameras that come with larger sensors also offer more restricted depth of field than those with smaller sensors.
In other words, all DSLRs are better than point-and-shoot digital cameras, but full-frame DSLRs are better than budget-priced DSLRs.
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