At 09:40 AM 6/2/99 +0200, you wrote:
>How does one overcome the problem of film surface curvature caused by
>inserting the film in a frame while scanning - without taking the film
>out of the frame? The film has a natural curvature, and sometimes the
>rather stiff frames cause even more shape distortion. In fact, the same
>problem appears on the projector, too. The overall shift from the plane
>is less than 1mm, but we're talking about 3K-something dpi...
>
>--------------------------------------------------------
>OMer Nezih Gerek
Hi OMer,
Very good question. I posed the same question to Nikon tech (I have LS-20e
film scanner) and they suggested glass mounts, which is impractical for
negative film IMHO. It's a little impractical even for slide film. What
one wants is something that is comparable to stopping down the lens on the
enlarger a little bit, but alas this cannot be with film scanners. It's
not a silly problem as EVERY piece of film is a little bit curved.
The best bet is to shoot slightly wide; don't crop too much in the
viewfinder so that the edges can be cropped sufficiently in the scanning
process to provide a satisfactorily sharp overall scan. I hate doing that
with slide film, but with negative film I make a conscious effort to
provide cropping room.
The Nikon scan software allows one to select specific focus points. If one
selects the default, it focuses on the center and one often notices that
the edges look soft. I usually don't focus at all and find that the
scanner does a good job overall and that sharpening in Photoshop produces
very acceptable results. If edges are soft, I select a point very close to
the edge for selective focus. This often makes both edges sharper without
softening the center too much. I don't know why this works. Perhaps
Phillip Franklin's observation that the CCD has enough DOF to provide
acceptable focus is what is operating here. If it has enough, it sure
doesn't have a lot! I just happened upon the method by trial and error,
and it is not a perfect solution.
Joel Wilcox
Iowa City, Iowa USA
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