Re: filmscanners: VueScan 7.2.11 Available

["Rob Geraghty" <harper@wordweb.com>]

"Julian Robinson" <jrobinso@pcug.org.au> wrote:
> I must not have explained myself well.  I understand that the problem is
> bowed film - I have a web page devoted to the issue.

OK, but having reviewed your web page, you're only talking about colour
negative strips in the motorised SA20 adapter.  The way the adapter
operates - pulling the strip the whole way in to measure the number of
frames, then feeding it back out when you scan frame 1 - tends to make the
end of the strip curl longitudinally.  What this means for me in practice is
I get a scan which is 3/4 in focus and 1/4 out of focus at one end.  This is
the *only* kind of noticeable problem I've had with DOF and my LS30, and
only if I have film that is curled before I put it in the scanner, or I
leave it too long so that that the heat of the scanner makes the plastic
"remember" its curl.

> I am only saying that while it seems intuitively that a diagonal offset
> from the centre should be best, I think that in practice an offset along
> the "y " axis, not far from the top or bottom edge is a better choice.

In the case of longitudinal curl of an unmounted strip, I agree.  But AFAICR
this discussion about DOF problems began with people who had curved *slides*
in old mounts, especially cardboard ones, which would be a hassle to
remount.  In a mounted slide, the curve (in my experience - YMMV) is
"bubble" shaped.  If you measured the focus at the edge of the frame you
would be in the wrong place.  If the curve is bubble shaped, ISTM the best
place would be halfway between the center and one corner.

I avoided this whole issue with film strips by using the film strip holder,
but it is painfully slow to use.  The IA20 APS adapter doesn't seem to have
the problems with curling that the SA20 does.

Your focussing measurements may have been affected by the amount of time it
would have taken to do.  As I mentioned above, I find the film curl tends to
increase the longer the film strip is in the scanner.

I can understand Ed not wanting to provide a point and click method of
determining the focal position when few scanners support it - Vuescan
supports an awful lot of scanners!  Perhaps one idea would be to have a drop
down list with at least three options - center, diagonal, edge.  Obviously
the options should only appear when the scanner supports setting the focal
position.  The problem with offset is which direction?  When I've seen the
curl problem, it has been the end frame of a strip, and the curl is closest
to the end.  This could happen at *both* ends of a strip, but I think it
mainly happens at the "front" end of frame 1 because that is the part of the
strip which is curled the most inside the SA20 in order to fit the strip
into the adapter.

I wish I had time to do more tests. :(

Rob