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[OM] Re: TOPE 36 call for entries, and extended shooting period

Subject: [OM] Re: TOPE 36 call for entries, and extended shooting period
From: WayneS <om3ti@xxxxxxxx>
Date: Mon, 10 Nov 2008 21:13:06 -0500
At 09:08 PM 11/10/2008, Fernando wrote:
>...
>
>How do you inspect the amount of dust on the mirror without disassemble? 
>I found useful a pair of small concave mirrors, those used by dentists ( 
>my father was a dentist .... )  to reflect light into the scanner, light 
>from a MagLite torch.

For me the sign was halos around bright areas of the image due to the dust
scattering the brighter light from the image.

So look a bright area of the image and see if the scan looks OK. Of course
bright halo effects might be in the film, but if they consistently show in the
scan, probably means the mirror dust is scattering light.

If you don't see any evidence of light scattering in the scan, examining
the mirror is not going to indicate much. The scan is the better indicator.
Poking around in the scanner for evidence is hit or miss. My first attempt
was to use a CO2 blower designed for cameras. That was only
marginally successful. When I had the mirror out, though, I used my
CO2 blower to purge as much dust as I could from the innards of the
scanner. There really wasn't as much dust as I was expecting.

I actually found some smudges, so it is possible some oil made it to the
mirror. I had to use some sensor smudge cleaner to clean it. Oil
is much worse than dust as it will distort and scatter much more,
and you will not be able to see it without removing the mirror.

Dust on the mirror is going to be out of focus, so it will either fog or
halo the bright areas of the image. Oil is another matter.

Another thought, when the scanner is sitting idle and not used, storing
it upside down may be best to prevent dust from settling on the mirror.
or even worse, oil. Oil lubricants are worse when the temperature is high.

WayneS 


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