Charts of Depth of field vs focal length, scaling f/#

Nodda Duma said:

Who says I left out magnification?

“Exact” means “did not leave any shit out”

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Yes, magnification is taking into account with "distance to subject, u" in your original post. I'm not sure what I was thinking when I made that post. I actually wrote a paper on depth of field in graduate school. How long ago was that...well I saved the text on a 5" floppy... As I recall we were not allowed to submit term papers printed out on dot-matrix printers, so had to have a 'typing service' re-type it to submit it.

One consideration that is usually neglected in most DOF discussions is that the CofC used in the calculation is typically something appropropriate for somewhat less than perfect vision...someone with 20/20 vision (as the optometrist in the US will correct your vision), can see CofC of that size on a 8x10" print viewed from 12" distance as blur circles and NOT perceive them as in focus 'points'.
The CofC size for 20/20 vision has to be SMALLER than typically assumed in most DOF calculators! The DOF zone depth is shallower when assuming 20/20 vision of the viewer, compared to the looser 'manufacturer standard' CofC.

I believe there is no difference of DOF between short and long lenses shot at the same aperture. It's an illusion because the CoC changes due to magnification and the angle each lens covers. The long lenses is magnifying the area raising the CoC so the DOF appear to be less. Since the shorter lense is taking in a much larger area, the area the long lens shot is only a small part of the shorter lenses angle enlarging the COC and making the out of focus area more out of focus. If you were to magnify the results of the short lens to cover the same area, it would have the same DOF.

Alan Edward Klein said:

I believe there is no difference of DOF between short and long lenses shot at the same aperture. It's an illusion because the CoC changes due to magnification and the angle each lens covers. The long lenses is magnifying the area raising the CoC so the DOF appear to be less. Since the shorter lense is taking in a much larger area, the area the long lens shot is only a small part of the shorter lenses angle enlarging the COC and making the out of focus area more out of focus. If you were to magnify the results of the short lens to cover the same area, it would have the same DOF.

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The exact comparison is provided in the charts above, and the math backs up what you’re saying for the case of magnifying to the same format print.

Alan Edward Klein said:

I believe there is no difference of DOF between short and long lenses shot at the same aperture. It's an illusion because the CoC changes due to magnification and the angle each lens covers. The long lenses is magnifying the area raising the CoC so the DOF appear to be less. Since the shorter lense is taking in a much larger area, the area the long lens shot is only a small part of the shorter lenses angle enlarging the COC and making the out of focus area more out of focus. If you were to magnify the results of the short lens to cover the same area, it would have the same DOF.

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Precisely. I have many times stated that the DOF is identical when I shoot the following

• 50mm f/5.6 at shooting distance 10'
• 100mm f/5.6 at shooting distance 20'
• 200mm f/5.6 at shooting distance 40'
• 400mm f/5.6 at shooting distance 80'

20/20 vision DOF zone on 8x10" print viewed from 12" is about 1.43' for all four shots, as the subject is the same size in all resultant prints.