Depth of field tables

[P3D Neil Harrington <nharrington@xxxxxxxxxxxxx>]

John Roll writes:

>I was wondering if anyone would have a table or formulas to find the depth
>of field for a 30mm focal length lens, focussed at 42cm from the subject to
>the film plane for f16.  

I can come reasonably close.  According to the depth-of-field tables in the
back of Arthur Cox's PHOTOGRAPHIC OPTICS, the depth of field for a 28mm lens
focused at 50 cm at f/16 is 39 cm to 70 cm, and for a 35mm lens under the
same conditions it's 41 cm to 65 cm.  That should put you somewhere in the
ballpark.

>I understand that the depth of field is dependent
>on the value of the circle of confusion.  

Which in turn is dependent on the degree of final magnification, which is
why all depth-of-field tables have to be taken with a grain of salt.  

>I would be happy with any
>reasonable value.  I also understand that the depth of field is usually 1/3
>in front and 2/3 behind the plane of best focus.  

Yes, but only at a certain distance.    :-)

That's an old rule of thumb which is probably better than nothing under
average circumstances, but shouldn't be taken too seriously.  Obviously
there are many situations in which depth of field extends to infinity, which
makes nonsense of the one-third two-thirds rule.  Contrariwise, as you move
very close to the subject the rule goes wrong in the other direction, i.e.
depth of field comes closer to being the same before and behind the plane of
best focus.



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