Re: pressureplate troubles

[Jaap Los <imagefotografie@xxxxxx>]

Gary Beasley wrote:
> 
> >From: Jaap Los <imagefotografie@xxxxxx>
> >Subject: pressureplate troubles
> >
> >- -Hi all,
> >I have used a #25 red filter and #87/#87C filters up till now. Of course
> >the IR effects are a bit stronger with the latter filters, but not very
> >much! However I noticed another difference between #25 and the #87(C)
> >filters -. Using a #25 filter I never had any ghost spots from the
> >pressure plate on my negatives. The pressure plate of my camera is
> >rather pronounced: there are two round sunk screws holding the plate.
> >Using the #87(C) filters I noticed very often round spots on my
> >negatives caused by these screws! My conclusion is, that #87(C) filters
> >easily cause pressure plate problems whereas #25 filters do not! Is my
> >conclusion correct and did somebody have the same experience? Also I
> >can't explain this.
> >Best regards,
> >Jaap Los
> >Alkmaar, The Netherlands
> >
> It's best explained by realizing the ghost spots are caused by reflections
> of infrared light, not visible light. The #25 filters have a high level of
> visible light in relation to the IR so in effect washes the ghost spots
> away. You may still find them in areas of very strong ghost spots that show
> with an 87 if you know where to look and the image is reflecting little
> visible light but lots of IR, (like a black synthetic cloth or wig).
> Gary Beasley
>


Gary,
Looks a bit logical to me, although I quite cannot see, that IR light
reflecs more than visible light as both will go through the filmlayer
and bounce against the pressureplate. Your theory is that the visible
light passing through a #25 filter will wash away the IR ghost images.
Yes, that sounds OK. Could we have some more opinions from the IR
experts on this LIST? Thanks for your response Gary!
 *
> - 
Best regards,
Jaap Los
Alkmaar, The Netherlands

See also my Infrared Photography Homepage specially made for you with
lots of information and links to other sites.
at:   http://home.wxs.nl/~losjb/

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