Re: filmscanners: Hazy bleed in hi contrast blacks on LS2000

[Harry Lehto <hlehto@oj287.astro.utu.fi>]

On Mon, 11 Jun 2001, David Hoffman wrote:

> At 5:06 am -0400 6/6/01, IQ3D@aol.com wrote:
> >with the results. Just recently however we have put through a batch of slides
> >with subjects against black backgrounds. The scans have all got a hazy halo
> >round all the bright areas
>
> I doubt that it's flare from dust or stuff (but you could give it a
> good blast with canned air to see). I've seen this with my LS2000
> too. It happens where there are large light areas next to black.

It is sounds similar to what I reported a while ago on a nikon cooslcan
IV  (ED40) and Canon 2710. I've since seen scans of a similar phenomenon
on LS 1000 and LS 4000 and also some other brand scanners that escapes my
mind.

> kind of electronic flare - CCD cells reaching a high enough voltage
> when strongly illuminated to induce a higher voltage in their neighbours.

The CDD leak should show always as artifacts (usually as streaks) on the
same side of the bright image (right?). And it should go away if decrease
the CCD exposure time. (At least this is the way it works in astronomical
CCDs).

The scanner itself has optical elements in it. And with these elements
comes reflections and other optical distortions. The black backgound
close to a bright spot is very unforgiving for such things. If your halos
move to the "outer" side of your bright image then I believe that it is
a reflection or a comalike distortion. If they stay only as "halos"
centered on your bright spot even right at the edge of your field then
I suspect some internal reflections in the optical elements closest to the
CCD.

You may want to check how these halos behave. Take a black film, make
severel dozen holes, and see how these halos behave in different parts of
the film.

Regards
Harry
hlehto@astro.utu.fi