Re: DOF @ a focal length

[T3D John Ohrt <johrt@xxxxxxx>]

T3D Peter Abrahams wrote:

>  Does anyone have a handle on
> how 2 lenses of the same focal length and aperture can have different DOF?
> The answer would likely give a clue to the question of how to make out of
> focus images sharper without stopping down.

Do I KNOW anything, probably not.  But acutance is measured by MTF and MTF as
I pointed out in an earlier post is influenced by glass quality, coating
materials and application quality, etc etc.  Since to define DOF you must
specify an acceptable circle of confusion ( substitute the term of your choice
), appartently identical lens can differ measureably in DOF, even from the
same manufacturer.

This is important in scitech work and carefully measured in many such
applications.  My impression is that the "artists" take a more lax approach,
since in many applications they can control aperture and exposure time to
achieve the desired DOF, ie. in many artistic situations requiring a
controlled DOF, the inherent DOF of the lens exceeds requirements.

--

John Ohrt * Toronto * ON * Canada






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