View Full Version : Fresnel Removal

Paul Mongillo
21-Aug-2000, 18:15
I have a Phillips 4x5. It has a Horseman international back with a fresnel atta ched. I initially was pleased with the brightness of the fresnel, but have begu n to think that it is more difficult to focus with it on. I would like to try s ome shooting without it, but am concerned about what affect removing it will hav e on how everything else is aligned. Any suggestions?

Doug Paramore
21-Aug-2000, 22:00
Paul: If the Fresnel is behind the ground glass, as I believe it will be, it will have no affect on the focus plane. You won't be changing the distance the lens focuses on. Store the Fresnel wrapped in something soft and placed in a box. The lens side is easily scratched. You may want to use it later or on another camera.

Regards, Doug.

Robert A. Zeichner
22-Aug-2000, 08:24
The business of behind or in front of the ground glass is somewhat confusing if, for instance, behind the ground glass means hidden by it! I prefer to state it this way: If the Fresnel is "between" the ground glass and the lens, removing it will cause a shift in focus unless the shims are changed. This of course assumes the assembly was designed in such a manner that the user has a choice of Fresnel or no Fresnel. I'm very familliar with that Horseman back and I do recall some black fiber shims that lie between the gg and the mounting pads. The Fresnel is actually "hung" on the gg between the gg and lens with some metal clips. It does not get sandwiched between the pads and the gg. One maker of an after market screen failed to notice that, which is how I became involved in gg alignment in the first place! If you want to conduct this experiment with assurance that you will be able to get back to where you started, make a drawing of where everything goes. I believe what you will need to do to compensate for the removal of the Fresnel, is to also remove the shims. Those shims should have a total thinckness of 1/3 of the thickness of the Fresnel, which I believe was around .0500" if memory serves me. You should then conduct a film test to confirm proper alignment. See my article in ViewCamera magazine, Nov./Dec. 1996 for instructions on making and using a ground glass test target. Feel free to email me if you have any questions.