26 May
2007
26 May
'07
6:05 p.m.
On Sun, 27 May 2007, Tony Duell wrote:
LEns resolution is worse at very small apertures due
to difraction
effects. But for close-ups where depth of field is limited anyway, keep
the lens stopped down (smallest aperture).
and, of course, it varies a lot depending on lens design. SOME large
format lenses (Goerz?) are specifically designed to be happy at f64.
An oversimplified rule of thumb is to avoid the last 2 stops at each end
of the range.
The right way to get better depth of field for oblique
shots is to tilt
the lens (!). There's a well known principle, the name of which I can
neither spell nor pronounce that basically says the image plane (film),
subject plane, and a plane throughthe centre of the lenx perpendicular to
the optical axis should all interstect in the smae line.
"Scheimpflug"
(Theodor Scheimpflug denied originating the principle that is named after
him.)
That said, it deptend on what you want to do with the
photos. If you want
to just keep a record of how something wnnt together, how the cables were
routed, and so on, then just about anything will do if it can focus close
enough.
You can also cheat with "Portra lenses". A 3+ portra lens will give you
focusing from about a foot down, and can be added to almost any camera and
lens. But, certainly nowhere near as good an image as an untampered lens
on an extension tube. For a 50mm lens, you're not likely to need more
than a few more millimeters, so a bellows is suitable for long lenses, or
extreme closeups. A quick rule is that adding an extension equal to the
focal length gives you 1:1.
--
Grumpy Ol' Fred cisin at xenosoft.com