Re: observations

[Helmut Faugel TE <htf@xxxxxxxxxx>]

On Wed, 10 Sep 1997, Wesson, Dexter L @EAG wrote:
> 2.  On my last vacation, I had an occasion two times to shoot a scene
> (without moving the camera, etc.) with Tmax, Velvia, and HIE.  The HIE
> shows
> a distinct aperture hexagon which is not present on either the Tmax or
> Velvia.
> 
> Both times the sun was high in the sky (I know , too contrasty, but I
> was on V)
> but not shining into the lens, i.e.  the lens was shaded.  Any ideas on
> what caused this?

The multicoating of the lens is optimised for visual wavelenght, in the
IR the coating does not work well and because of that its possible that
internal reflections are not visable on normal film, but the appear on
IR-film. I remember a chart published by Heliopan which shows the effect
of multicoated filters, from 400 to 700 nm the loss of light is less 
than 1% but at 800 nm it is almost as bad as an uncoated filter. The
losses in transmission are caused by reflections at the surface air/glass.


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Helmut FAUGEL                       |  I hate getting junk mails ...
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