On Jan 4, 2006, at 4:24 AM, Jostein wrote:
If you plan to use the lens without reversal, you should pick a
macro lens. The
macro lenses can cope with a lot of extension without significant
quality
deterioration.
It's not altogether necessary to reverse mount a lens to get good
results. It helps a lot with non-macro lenses, flat subjects, and
relatively high magnification.
You will find that with long extension on the bellows, the
viewfinder will grow
very dim. It will be difficult to focus in low light, even with
lenses like a
50mm f/1.4.
Focusing at high magnifications is a bit of an art, takes practice. A
geared micro slider platform for the camera makes it much easier.
I don't know how to compute the magnification you get by simple
extension, but
with a reversed lens, the math is simple. Divide the extension in
mm by the
focal lenght of the lens.
It doesn't matter whether you use a lens reversed or not, if the lens
is a near-symmetrical design. Same formula works for either case. For
telephoto or inverted telephoto designs (not symmetrical), the
problem is that the effect of extension is non-linear.
More seriously, you need to determine where the lens' nodal point is
located as the correct distance measurement is from lens nodal point
to film/sensor plane.
My favorite easy reference for this is the Kodak Professional Photo
Guide from 30 years back. It has an excellent, easy to use calculator
and a list of formulae for magnification, exposure factors, etc.
Be sure you have a sturdy, rigid tripod and a remote release or use
the self timer.
Godfrey
