[filmscanners] Re: Calibration issue

["Mark Crabtree" <cirkut@adelphia.net>]

>>But the question is, shouldn't calibration take care of this? I
>>thought that was what calibration did.
>
>I'm not all that knowledgeable on these things, but had wondered if
>the tube was
>producing the uneven illumination.  If its both then it sounds more
>like it could be the
>mirror or a lens is dirty.  I've always assumed calibration was on
>the total sensor array
>not point by point.  Here is where we need an expert to come in :-).

I wish they would. I know there's a couple guys out there who know
this stuff. It's just out of my league, and who else can you ask.
Good luck talking to Umax; they'll barely help you with a new, under
warranty, scanner.

My understanding is that calibration adjusts for uneveness across the
tube, but since it is going through the lens/mirror and everything
should also correct for uneven illumination from whatevr cause. I
think it reads a white target in reflective mode, and the light
source itself in transparency mode, then fudges the numbers so that
it comes out evenly illuminated all the way across. That's why if you
get a piece of something in the calibration area, you can get a weird
line in that part of the image. Hey, maybe I should try that as a
test.

These lenses do fall off in performance at the edges of the image and
I wouldn't be surprised if the tabloid size is worse. Nonetheless,
this was an expensive scanner when new. They claimed to target it at
pre-press and bragged about how many slides you could scan at once.
So surely it should be more even than this.

Mark

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