[filmscanners] Re: My Public Apology

["Arthur Entlich" <artistic-1@shaw.ca>]

Anthony Atkielski wrote:

> Arthur writes:
>
>
>>On my monitor, there is some distinct, what
>>appears to be Newton Ring color distortion in
>>the sky of this scan.
>>
>
> Yes, I see it, now that it has been pointed out.  I see another ring up near
> the condensation trail in the sky.  They are pretty faint on my monitor,
> albeit difficult to ignore once noticed.
>
>
>>It is quite noticeable in the sky in the middle
>>of the Eiffel tower and just above the right-hand
>>building closest to the tower.
>>
>
> It does not seem obvious on my monitor (or to my eyes).  I hope this does
> not mean a problem with the monitor (which is several years old).  I try to
> calibrate it regularly.
>
>
>>Was a glass carrier used to scan this image?
>>
>
> Yes.  It greatly improves the focus, but I have to blow a hurricane of
> compressed air over the carrier and film to try to keep them clean, and as
> you can see, I'm still getting interference.  These rings don't look like
> dust, though--more like a slight flexing of the film, or something.
>
> I'm open to suggestions on how to get rid of this.  The glass carrier for
> the 8000ED already contains anti-newton glass, and I blow everything clean
> over and over.
>


I did notice a hunk of dust or dirt up above somewhere as well... but
that's an easy clone.  Personally, I'd probably have removed the jet
streak as well, but I'm not a purist.

The cause of Newton rings isn't dust, in fact dust might help prevent
it.  Printers use a very fine anti-Newton powder between negatives and
glass, especially with large format negs.  As you probably know Liths
are usually made 1:1 of the plate size, which makes a very big and
basically physically unsupported film, so they use a vacuum mount with
Anti-newton powder. Today this is less common as they have gone to
"direct to plate systems via digital methods.

Newton rings occur when two very glossy surfaces come in close contact
with one another.  Basically, the distance between the surfaces becomes
so small that the light reflects between the two surfaces. The rings are
the result of interference patterns when the separation between the
surfaces equals some order of wavelengths of visible light.

The way to avoid them is to keep the surfaces separated with enough
space, or a randomized enough space to not allow these interference
patterns to occur.  Anti-newton glass has an etched pattern of
undulations on a microscopic level.  Sometimes, unfortunately, they
become visible when doing high res scans, so the level of etching can't
be too drastic.  Of course, the less drastic the etching, the more
likely the prevention won't be totally effective in removing all the
Newton rings.

The things I would try to do to reduce Newton rings with anti-newton

glass is to try to avoid excess pressure of the glass against the film,

Make sure the film is completely dry and oil free, and that the glass is
as well. I'd be less concerned about dust and dirt since you have dICE
with your scanner.


Art


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