[filmscanners] Re: CanoScan 9900 & "Dirty" Glas Plate

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

This problem is often due to the plasticizers or mold release agents
evaporating from the plastic surfaces from heat after the scanner is
built.  SOmetimes even the materials used in packaging the scanner may
off-gas materials that deposit of the glass bed.

These scanners travel by slow ship and often go through considerable
temperature changes.

First, make sure the fogginess is on the inside surface, by carefully
cleaning the outer surface well.

As to how much the fog degrades the image, it somewhat depends upon the
degree of "fog" the type of lighting and image sensor, and the thickness
of the glass.  If there is an area, as you indicate, which is not foggy,
you may wish to scan the same material in different areas of the scanner
and see if the results are different, keeping in mind that all flatbed
scanners have a "sweet spot" where they scan the best (usually a column
down the center of the length of the scanner bed).

The bottom line is that scanners really shouldn't have residue on the
internal glass surface, and this should be covered by warranty.  You
might try an exchange and see if the next one is cleaner.  Sometimes
service techs will end up removing the fog during a cleaning but add
other dirt or contaminate the image sensor.  These scanners are put
together by robots and people in clean rooms (in theory, at least) and
whenever they are opened, the risk of new dirt entering exists.

Art


Robert Meier wrote:

> I have just purchased a CanoScan 9900. After installing the unit I realized
> that the glass on which the film/document is placed is "foggy". You can see
> this best when the scanner light is on and look almost parallel to the glass
> plate. The part closer to the back is more "foggy" then the other side. Also
> there is a small clear part so it's definitely not just a property of the
> glass. Has somebody else discovered that on this particular scanner or other
> scanners? Is this typical? Does it affect image quality from a practical
> point of view?
>
> Robert
>
>

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