Nikkor 35mm and HIE - strange hexagonal reflections

[Eckhard Stephan <eckhard.stephan@xxxxxxxx>]

Hello,

on some HIE-pictures I shot recently, I found a strange hexagonal area
of slightly higher density in the middle of the frame. You can see an
example at http://www.eckhards-photobox.de/HIE.jpg . (Sorry for the
lousy quality, I simply scanned the neg on a normal office scanner...).
The hexagon only occured with a used Nikkor 35mm 1:2,8 lens that I
recently bought and that works well with non-IR films. The higher
density area was stronger visible with a Heliopan RG 780 (=Wratten 87)
than with my red #25. Other lenses than the 35mm performed well, so I
think it is a problem with this special lens, not with the camera (a
Nikon F3). My first idea was, that light was reflected from the
backplate on the aperture blades and from there back on the film.
However, in this case the hexagon would have shown less density than the
surrounding areas, wouldn't it? Flares can be ruled out, since I had the
sun directly in the back an the camera's viewfinder was covered with the
built-in curtain.
Any ideas what it might have been?

Thanks in advance,

Eckhard

-- 
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*          Eckhard Stephan             * 
*          Freiburg (Germany)          *
*     eckhard.stephan@xxxxxxxx         *	
*   http://www.eckhards-photobox.de    *   
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