>From below


DOF in mm      ~= Stop x distance /  Focal length / 2

DOF in inches ~= Stop x distance /  Focal length / 50


For distance to subject and focal length in consistent units but which
do not have to be the units that DOF is stated in :-).

DOF is smaller for people with good eyes or in brighter light!!!


E&OE !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

===================================================


>> I'm guessing he's not seeing diffraction effects as much
>> as sensor noise. Diffraction is a rather subtle effect, and
>> unlikely to be a major issue at f/14.

> I'm afraid, diffraction could be the major issue at f/14. Though I
> must admit I got no experience in this area and I don't plan getting
> any.

I find I can typically use f22 without noticeable diffraction
softening. It's probably there but largely  swamped by other issues in
the lens class I deal with. [Approaching OK by my standards, more than
expensive enough by my wife's standards, far short of what the
professionals usually buy with perhaps one exception].

f32 works and can be sharper than with a larger  aperture in some cases.

Mr Wikipedia says:


When the depth of focus relates to a single plane in object space, it
can be calculated from[1]

       DOF =  t = 2 N C V / f

where t is the total depth of focus, N is the lens f-number, c is the
circle of confusion, v is the image distance, and f is the lens focal
length. In most cases, the image distance is not easily determined;

"Circle of confusion" ~~~= largest area you perceive by eye as a point
and not a finite sized spot.
Thus COC is subjective depending on observer, lighting and viewing distance.

A typical value is 0.2mm based on a typical viewer viewing an image at
250 mm and  resolving 5 line pairs per mm. The size of image which is
comfortably viewed at that distance is determined by viewing angle
being 60 degrees max and is about an 8x10" or A4 print.

SO    DOF = 10 x f_stop x image distance / focal length.

So  DOF increases linearly with f_stop( decreasing aperture), greater
image distance, decreasing focal length.

For say  f 1:16, 50mm Focal Length , coc = 0.2mm

DOF = 2 x fstop x COC x Distance / Focal length *

DOF =~~ Distance / 8

So for Vitaliy to get 1" DOF he needs about 8" distance from object.
Image size will be set by above parameters + distance.

Double f = double DOF
Double distance =  double DOF BUT area of image will decrease x 4 times !
Halve focal length = double dof.

To get large image size you want to focus at minimum distance at the
focal length of choice and then control aperture.

******************************************************************
* Usefully:

DOF ~~~ 2 x fstop x 0.2 x Distance / Focal length.    mm

or

DOF = Stop x distance /  Focal length / 2      millimetres
       =  Stop x distance /  Focal length / 50    inches

**********************************************************************
Sanity check.
f16, 8 inches = 200 mm, 50mm lens
DOF = 16 x 200 /50/2 = 32 mm ~~~~= 1 inch as above.

More accurate than that is not possible due to the immense uncertainty
from the COC.


          Russell















the depth of focus can also be given in terms of magnification m:
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