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[filmscanners] Re: depth of focus in scanners & old Kodachromes



Thomas,

Thank you for an interesting technique and the insight on Kodachromes...

Preben

----- Original Message -----
From: "Thomas Robinson" <tom@historicphotoarchive.com>
To: <krille@tin.it>
Sent: Sunday, March 31, 2002 8:40 PM
Subject: [filmscanners] depth of focus in scanners & old Kodachromes


I scan historic Kodachromes, which are often badly warped.  I have SS4000
and VS.  I borrowed an idea from the Leitz Focomat enlarger.  This works
great on warped slides.  I remove the film from the mount.  I use one
anti-newton ring glass out of a Gepe slide mount and put it on top of the
slide.  I use #5 or 6 frames in the Polaroid film holder because they have
full borders.  This puts glass on top of the slide to flatten it, but none
underneath between the scanner and the image.  No matter how bad the slide
is, the scan is tack sharp from edge to edge.

>From February 1939 to about 1952, Kodak put a varnish on the processed
slides to help prevent scratches.  (after that time, the processing was
modified and the emulsion was chemically hardened).  I have been using
Edwall film cleaner to remove the varnish.  Removing the varnish helps
considerably.  I heard from National Geographic last week that they use
Anchor P-150 PIT-GO Film clean to do this.  (the change in processing was
accompanied by a change in the mount.  If you have a red-back Kodachrome
with two lines of text, you can assume that 99% of them are varnished.
One-line redbacks are 100% varnished.  The white back I have never seen
varnished.)

I bought Vuescan,  Silverfast full version and downloaded the new Insight
scanner programs, and spent days comparing them.  Vuescan gave the best
shadow detail of any of them.  The early Kodachromes are very contrasty.

I bought several extra film and slide holders for the SS4000 on ebay and
have made modified holders for odd size slide films, including the 828
bantam size (looks like a 35mm but is a little larger) and the
pro-instamatic square size.

Thomas Robinson

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