From: Les Newcomer (lnphoto@ismi.net)
Date: 02/01/00-04:31:20 PM Z
Judy,
I'm not a computer expert, won't claim to be even when on heavy cold medication
as
I am now. But you got me to wondering about just how much depth of field my
scanner
has (HP 4c) So I devised a down and dirty test that I'm sure somebody will
shoot
down, but here it is.
I took a 16" stainless steel ruler and taped it to the top of the cover of the
scanner. I then placed a 1" wide roll of tape so it fell on the 10" mark. The
ruler now runs on an incline at 1/10" per inch on the ruler. i.e.: the 5 inch
mark
is .5" off the glass. I scanned it a 400% and then viewed it on my sreen in
Photo
shop at 100%.
Results: The 0 mark was nice and crisp. The 1" mark had a shadow on it (engraved
ruler reflection) but still looked sharp. the 1.5" mark had lost the distiction
between the shadow and the black mark itself.
Conclusion: My scanner has a rough depth of field of .1 to .15" above the glass.
Beyond that it's a portrait scanner
Les
Judy Seigel wrote:
> On Tue, 1 Feb 2000, Tom Ferguson wrote:
> > ... Many scanners (including mine) have holders that
> > elevate the film a few mm above the glass. Unfortunately with large format
> > film, the center often sags just enough to get a few rings in the center of
> > your picture ;-(
>
> I was wondering if any of you scan experts know if difference in focus
> is an issue when elevating/not elevating. For instance I have put slides
> in the mount on the scanner bed, also a holder comes with for 4x5s, but
> I've also scanned a large negative with no holder directly on the glass...
> not noticing focus or Newton problems with any, but not looking for them
> either.
>
> I've found that the copy machine seems to have a depth of field so that
> small differences (eg a pasted-on cardboard) come in equally sharp. On the
> other hand, when I've *scanned* 3-dimensional objects I've found that they
> get out of focus within a relatively short distance.
>
> Presumably the scanner is configured to be sharp for opaque copy directly
> on the glass and, unless works differently for negatives in holders, has
> that amount of leeway, but, as noted it goes off before a great distance
> is reached. I also note that I had trouble with a quite curly fiberbased
> print until I weighted the scanner cover -- not so much sharpness as I
> recall, as tone, which was woozy.....
>
> Any input on these issues gratefully received. (We the damned of scanner
> hell need any help we can get... And PS to faithful friends & readers:
> The THIRD scanner replacement was also defective !)
>
> PS to Tom: Beseler I believe has a glassless negative holder that grabs a
> large-format negative with pins of some sort around the edges and holds it
> tight. It's fairly thick, but I wonder if something of the sort could be
> configured to hold your large neg flat.
>
> Judy
>
> >
> > You rarely see this problem scanning prints due to the fact that paper
> > (printers or photo) is rougher (less glossy) than film.
> >
> > On my Umax Powerlook, I find a lot less newton rings with the emulsion down
> > towards the glass. I assume that this side is less smooth, and thus less
> > rings. In the original software I had to flip the image (as the scan was
> > backwards). In Umax's newest drive it is already set for me (confused the
> > heck out of me for the first week!).
> >
> > Hope that helps.
> > --
> > Tom Ferguson
> > http://www.pipeline.com/~tomf2468/index.html
> >
> >
> > > From: Dave & Erin <dfisher@nstar.net>
> > >
> > > My name is Erin and I am a grad student and I scan a lot of my negs. The
> > > moire pattern is common when scanning negatives. At school I am using a
> > > Linotype scanner and it came with a liquid solution that you put some on the
> > > scanner and then lay your negs down and it prevents the moire pattern.<SNIP>
> > >
> > >> From: Kathryn Garrison <Kathryn.Garrison@Colorado.EDU>
> > >>
> > >> I'm hoping someone has the answer to this, I have a negative with some kind
> > >> of damage to it... not sure what. Although I'm not able to see it through
> > >> the loupe or projected from my enlarger, when I scan the negative there's a
> > >> distinctive moire' pattern.
> > >>
> > >> I'd like to have a scan of this negative! Does anyone have a suggestion? I
> > >> recall that oil is sometimes used with microscopes to improve the image,
> > >> would I be further damaging the negative if I did that? Kathryn
> >
> >
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