[LargeFormat] fresnel screen orientation

[Vincent Dobson]

Thanks Richard, good info.

  I have one question.  If I put the fresnel under the ground glass of my
Tachihara, that puts the rear of the GG further from the film plane by the
thickness of the fresnel.  Does the fresnel compensate for this in some way?
I always worried about that but that is the way Beattie instructed me to do
when I got the Fresnel.

Vince Dobson
Visions In Nature
www.VisionsInNature.com

::>>
:>  What you have is the ideal set up where the back has been
:>designed for it. This is also the orientation of Graflok
:>backs. The idea is that this arrangement, fresnel surface
:>against the glass ground surface, has the least internal
:>reflection and the least spreading of light after the
:>fresnel. Most camera backs reference the ground surface of
:>the ground glass so the fresnel must be placed on the back
:>of the camera in order that it not shift the focus reference
:>plane. Where the fresnel is on the back the grooves should
:>face the ground surface of the ground glass to minimise
:>internal reflections and scattering. So the rule is that the
:>grooved side should fact the ground surface whatever the
:>location of the fresnel.
:>  The idea of the fresnel lens is that it focuses the light
:>normally scattered by the ground glass surface back toward
:>the eye.
:>
:>---
:>Richard Knoppow
:>Los Angeles, CA, USA
:>dickburk@ix.netcom.com
:>
:>
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