Re: filmscanners: Dust in Sprintscan 4000?

[Arthur Entlich <artistic@ampsc.com>]

> "If, instead, the "dirt" is really chemical compounds or small partially 
>dissolved pieces of emulsion, then ICE probably wouldn't help as infrared 
>light would pass through it as easy as
> the film itself.  If anyone with ICE notices this type of "dirt," you might 
>report to us if ICE is of any use.  This is all really quite irrelevant 
>because no lab should embed any kind of dirt in
> the emulsion.  If you see it, tell you lab about it and insist that they do 
>something about it."
>  
> If the impurity can be "seen" by infrared light (including embedded dust in 
>the emulsion, and defects in the film) then Digital ICE will identify the 
>defect and attempt removal, usually
> with success.
>  
> Jack Phipps
> Applied Science Fiction


I've raised this query before, and perhaps it needs some further
exploration. 

Obviously, a lab which is not caring properly for the film, either
creating physical damages via handling, or not filtering their chemistry
and air properly, and causing defects in the film, is one issue, and the
fixes are well documented in lab manuals.

But, is it possible scanner CCDs are responding to some information
which is normally outside of the "visual spectrum", or are, due to some
type of lighting or optics issue in the use of separation filters,
emphasizing defects in the emulsion or base layers (perhaps microscopic
air bubbles or density changes that show up as defracted light patterns)
which end up looking like "spots" or dots on the scan? For instance, I
notice some films, when viewed on certain angles, have an almost
crystalline quality to the base surface.  This is not, as far as I've
been able to determine, a residue on the surface, but something within
the structure of the film base itself.

Further to this discussion, is it also possible the infra-red scans
"see" things that aren't optically there, again, I'm speaking of
elements which show up as opaque in the infrared spectrum, but are not
visible with white light?  If this were the case, digital cleaning
methods using IR might remove "defects" which were not there, causing
another type of artifact.

Lastly, how much residual silver ends up within the processed C-41 or
E-6 film?  Can there be any redepositing of silver during the process
which might explain these very tiny spots?

Art