I save this mail for when I will understand it! thank you all for your advices.
Danilo. On 1/5/06, Godfrey DiGiorgi <[EMAIL PROTECTED]> wrote: > > 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 > >
