# Circle of confusion for nikons dof scales

Discussion in 'Nikon' started by Marc Wossner, May 27, 2007.

1. ### Marc WossnerGuest

Hi,

calculating the circle of confusion for the depth of field scales of
my nikkor lenses with the equation from norman korens website (http://
www.normankoren.com/Tutorials/MTF6.html#DOFscale - C = f^2 / Nmax * (s-
f)) I found that they differ throughout the focal lenghts:

f/3,5 18 mm = 0,044 mm
f/2,8 24 mm = 0,069 mm
f/2,8 28 mm = 0,037 mm

I´m quite astonished in finding a) such huge differences and b) values
so far apart from the industrie standard criterion of 0,032 mm. Can
anyone confirm those findings?

Best regards!
Marc

Marc Wossner, May 27, 2007

2. ### Alan BrowneGuest

The DoF markings on a lens are for guidance, not absolute results.

If you "lock" some variables then other variables like CoC have to
change. But that's probably not what you're looking for.

The "standard" is typically based on a print size of 8x10 (inches)
viewed at about 12 - 18" away, and this what is reflected in the DOF
scales on 35mm and AFAIK most (all?) MF lenses.

The CoC that you "want" is properly driven by the enlargement ratio from
the film to the print. The greater the enlargement ratio, the smaller
CoC you will want in which case the DOF markings on the lens are not
tight enough. ... unless the larger print is viewed even further away,
in which case it's a wash.
The industry standard CoC for 35mm is actually closer to 0.025mm for the
"reference" print size.

Again, CoC should be driven by your preferred print size not the lens
markings ... unless of course you always print at about 8x10".

Cheers,
Alan.

Alan Browne, May 27, 2007

3. ### Paul FurmanGuest

This is three different lenses? The 2.8/24 just isn't sharp? Or I guess
it's just different people designing the DOF scales over the years...
also many lenses are not exactly the focal length they state, the stated
length is often just a rounded number for simple labelling.

Paul Furman, May 27, 2007
4. ### Marc WossnerGuest

On 27 Mai, 19:07, Alan Browne <>
wrote:

You´re absolutely right and I wasn´t looking for that.
I was just trying to figure out the value the dof scales that my
lenses rely on
to be able to set aperture right for my desire.

Best,
Marc

Marc Wossner, May 27, 2007
5. ### Marc WossnerGuest

But it´s one manufacturer and therefore I was expecting one value.
You mean the rounding can change the value so far off?

Best,
Marc

Marc Wossner, May 27, 2007