ILUV767 From United States of America, joined May 2000, 3142 posts, RR: 7 Posted (14 years 1 month 3 weeks 5 days 22 hours ago) and read 2198 times:
I am in a begining photo class at my school, and I was wondering if one of you could give me a solid definition for depth of field? What factors affect it? I have very little understanding of it, and I have a test on it tomorrow.
PUnmuth@VIE From Austria, joined Aug 2000, 4164 posts, RR: 52
Reply 1, posted (14 years 1 month 3 weeks 5 days 22 hours ago) and read 2181 times:
Depth of field is mainly influenced by the aperture you are using. The higher the number the more depth of field the lower the number the less you get.
Depth of filed describes which parts of the picture are in focus. Low depth of field: The main subject you are focussing on is sharp and the fore and background are unsharp. Higher depth main object you are focusing on and parts of the fore- and background are sharp.
Jan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 46
Reply 2, posted (14 years 1 month 3 weeks 5 days 22 hours ago) and read 2170 times:
Factors affecting depth of field are:
1. Aperture (Peter described this)
2. Focal length (The longer the lens, the shorter depth of field)
3. Focusing distance (The closer the object, the shorter the depth of field)
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Cfalk From , joined Dec 1969, posts, RR:
Reply 4, posted (14 years 1 month 3 weeks 5 days 13 hours ago) and read 2149 times:
Depth of field (or DOF) is, as stated above, a measure of how much of your picture will be in focus.
No lens will have everything in focus, from a section of chain-link fence touching the lens right out to infinity. when you focus on an object, say 10 feet away, you may have, for example, everything between 8 and 15 feet away in focus, but the horizon and stuff in the forground less than 8 feet away is blurry. In this case, you depth of focus is 8 to 15 feet. Most old SLRs and some new ones have a function which will actually let you "preview" the depth of field.
Depth of field depends on 2 things: 1) the design of the lens, and 2) the aperture that you use. (Shutter speed has in itself no relation at all to depth of field.) The first one, you can't do anything about (other than buy another lens). But the second you have control over. The larger the aperture (which is equal to low f/stop numbers, like f/2.8), the smaller the depth of field will be. Portrait photographers often use lenses with very wide apertures, as it allows them to have the subject in focus, and all the backgroud be totally blurred, which prevents background feature from distracting attention from the subject.
A small aperture (equal to a high f/stop number like f/16) will give you a much larger depth of field.
If you focused on a specific object at 10 feet away, at f/2.8 your depth of field may be in the range of 9 feet (inner-limit DOF) to 12 feet (outer limit DOF). At f/22, your depth of field maybe from 2 feet to 60 feet.
Note when you look at the focusing distances on your lens (any lens) are not linear, but logorithmic. This results in that as your depth of field changes by changing the focusing point (keeping the f/stop constant) the distance in absolute terms of your outer limit DOF changes faster than your inner-limit DOF. Theoretically, the inner and outer limit DOF will intersect right in front of the lens, 0 inches away.
One concept that very few people use because of the popularity of rotating ring-type zoom lenses is hyperfocal distance, which is immensely useful, as it eliminates any calculation or trial and error needed to get the correct depth of field. Tell me if you want a description of that. But you won't be using that if you use most zoom or AF lenses.