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Re: filmscanners: Stellar ghosts and Nikon Coolscan IVED (LS40)



On Thu, 10 May 2001, Harry Lehto wrote:
> www.astro.utu.fi/~hlehto/nikotest/crop0016.JPG and
> www.astro.utu.fi/~hlehto/nikotest/crop0020.JPG

Rob:
>Dumb question; I presume they aren't in the source image as reflections
>in the telescope elements? I get similar ghost images when I photograph
>the moon.
>Otherwise presumably they must be reflections in the lens elements of the
>scanner. :-7

The original slide are good with no apparent ghosts. They were actually
taken with 50mm and 300mm camera lenses. Checked with a good slide
projector and separately with a microscope that the originals are OK.
These ghosts behave similarly to a coma in the sense that they appear
to become more pronounced and more separated from the true star as
one moves away from the slide center. Note that the .jpg images above
are not full scans but only corners of the slide.

Regarding Ed's fast reply I doubt that this is CCD bleeding, at least
it looks very dissimilar to the bleeding I see in astronomical CCDs.
I would expect this to happen along the CCD columns that are read off the
CCD, whereas even in the images that I have posted the ghosts are at a
tilted angle to the columns read.

I first though that they could be some kind of reflections from the
different dye layers of Kodachrome, but as they appeared also in
Ektachrome and Fujichomes that theory went into tha trash can.

Regards
Harry





 




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