[filmscanners] RE: "Halo" Effect

["Laurie Solomon" <laurie@advancenet.net>]

I will jump in unasked with a suggestion.  Before giving up on your film
choice or even on the SS4000, I would suggest you first do one or both of
two things to check and see if it is the film or the scanner, your
particular scanner versus SS4000 in general that is the soure of the
problem.  One thing would be to scan the image with another scanner and see
if you get the flares and halos; the second would be to see if you can find
another SS4000  to try scanning the image on to see if the same thing
happens.

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Joe Pedit
Sent: Thursday, August 22, 2002 6:03 AM
To: laurie@advancenet.net
Subject: [filmscanners] "Halo" Effect


Hi Art,

Thank you for your comments.  I left out some additional information for
the sake of brevity in my original post.  I also scanned the slide
(Provia 100F) in different orientations (e.g., sideways, upside down,
reversed) to check if the blue and red flares were a scanning artifact.
  The flares noted in my original post do not follow the stars when the
orientation is changed.  Instead, their size and location is always
proportional to the vertical distance from the centerline as seen by the
scanner.  In the original scan, a star located near the center of the
left edge would not have the red and blue flares.  When the slide is
rotated 90 degrees clockwise, from the point of view of the scanner the
star is now located near the center along the top edge.  That star would
now show the red and blue flares when it did not in the original scan.
It was based on this additional information that I assumed the red and
blue flares were a scanning artifact.

I would like to use slide film (E200, Provia 100F and 400F) for my
astrophotography because of its higher contrast, lower grain, and lower
reciprocity failure compared to color negative films (Supra 400, Royal
Gold 400).  Unfortunately, the flares and other problems associated with
scanning dense slides make the use of slide film difficult with the SS4000.

Joe


> Making the assumption that because the halos are visible with you SS4000
> with slides and not negs, does not prove the source is the scanner, in
> fact, it might suggest the opposite (;-)).  You need to check those
> slides with another type of optical system and make sure those halos
> aren't indeed on the slide, caused by the telescope optics.  Negative
> film may just be more forgiving of recording halos that slide film
> records, so it may simply be the nature of the way the film is responding.
>
> You may indeed be correct that the slide scanner is doing it (I don't
> shoot these kind of images, so my experience with slides with this type
> of contrast is very rare), but the testing needs to be done differently
> to isolate that.
>
> Art




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