No, changing the aperture of the lens does not affect its focal length
(changing the focus setting does) and I can't think of any technical
merits in focusing with the lens stopped down. In fact, the primary
advantage of a faster lens is its ability to project a brighter image
-- at its widest aperture setting -- which helps improve focus
accuracy. This becomes even more noticeable when you're printing color
negatives.
Berg
[EMAIL PROTECTED] wrote...
I own EL-Nikkor 50 f2.8 and 80 f5.6 lenses. Given that enlarging
lenses are used at around f8 most of the time, I doubt that the f2.8
is worth trading 'up' to from the f4. Especially if you bear in mind
that you should focus through a grain magnifier at the exposing
aperture-i.e. f8 for critical sharpness. Focussing at maximum aperture
and stopping down will cause a small loss of grain shrpness due to a
focal length change in the lens. Try it with a grain magnifier at 2.8
and 8.
Stewart.
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