DEPTH OF FIELD of Photographic Cameras
Quote: Most photographers accept the common belief that short focal length lenses have greater depth of field than do long lenses. A wide angle lens, in other words, will give greater depth of field than will a telephoto. Right?
Sounds about right, but it's not the case. In fact, if the subject image size remains the same, then at any given aperture all lenses will give the same depth of field./Unquote
Recently I found the following commentary on the web:
Well, it does not only sound about right' but it is dead right. In fact, if the subject image size remains the same, then at any given aperture all lenses will NOT give the same depth of field. I am not a professional photagrapher but as an engineer I believe in PHYSICS, OPTICS and the related MATHEMATICAL EQUATIONS, and based on these it can be easily shown that with decreasing focal length the depth of field increases considerably under the cited conditions.
I do not want to bother anybody with the related Math. The table below should prove my and most photographers 'common belief ' to be right.
Focal
Length
[mm]
45
15
5
Distance
[meters]
f-stop=2.8
9
3
1
Near Focus
Limit
[meters]
Far Focus
Limit
[meters]
6.39
15.22
1.35
0.21
Infinite
Infinite
45
15
9
3
1
4.95
0.87
0.12
49.24
Infinite
Infinite
45
15
5
9
3
1
3.45
0.52
0.06
Infinite
Infinite
Infinite
f-stop=5.6
f-stop=11
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( Circle of confusion = 0.033mm. The distances were selected to obtain the same subject image size.)
5.
DOF Calculator for Windows
Many digital cameras have typically a focal length of around 5.4mm - 16.2mm. These small values make focussing rather unproblematic because of the large depth of field..
On the negative side is the fact that it is rather difficult to obtain artistic pictures with the subject in focus and a completely blurred background.
This site gives some hints how to solve this problem:
Password: rainer
A DOF Program
for the
HP48SX/GX
Calculators
and for
EMU48
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