In the Canon Professional Newsletter (CPN) July 2009 you can find a technical article titled Tools: Depth-of-field calculator
It defines briefly the depth-of-field concept and how the former can be applied in photography. For example isolating a subject through a shallow depth-of-field. Furthermore it deals with the variables you need to take into account when calculating the depth-of-field such as the Circle of confusion. The Circle of confusion represents the largest blurred circle that can still be clearly defined by the human eye from a given distance.
Some assumptions were made to develop the calculator.
About the calculator...
You can select your EOS Canon camera, fill in the focal length, select the f-stop and finally the focus distance. The calculator will immediately tell you the 'Near limit of focus', the 'Far limit of focus', the 'Total depth-of-field' and the 'Hyperfocal distance'.
I'm shooting a lion somewhere in Africa with my 400mm, the distance between the lion is more or less 15 metres, the aperture is 2,8 and the body is a EOS 1D-MarkIII.
So the Depth-of-Field calculator says:
Near limit of focus: 14,9 m
Far limit of focus: 15,1 m
Total depth-of-field: 0,23m
Hyperfocal distance: 1905,2m.
The conclusion might be that the Total depth-of-field is too shallow here and it would be recommended to have a smaller aperture. For example f/5,6 generates 0,46 metres and f/8 0,66 meters.
Notice that the hyperfocal distance is 1905,2 metres; focus at 952,6 metres and things are sharp between 952,6 metres and infinity.
A 350D body with a zoom lens at focal length 22 mm and the aperture is f/8. The subject distance is 4 meters.
Depth-of Field calculator:
Near limit-of-focus: 1.78m
Far limit of focus: Infinity
Total Depth-of-Field: Infinite
Hyperfocal distance: 3,21 metres.
So everything between 1,605 metres and infinity will be sharp here.
I'm photographing a small bird such as a weaver approximately 4 meters away with a 400mm lens at an aperture f/2,8. This will generate a Total depth-of-field of 0,01 meter.
Through this calculator you'll quickly see that for example f/8 @ 6 meters is much better as you'll 0,08 meter room which will result in a sharper bird overall.
In my opinion this Depth-of-Field Calculator tool is a very useful and efficient tool as it just gives you an idea of the amount of depth-of-field you will have in certain situations.
Threaded view TrekNature forums Depth-of-field calculator.