[pure-silver] Re: [OT] Filmholders, Septums, Total-Disasters

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Fri, 25 Nov 2005 13:33:24 -0800


----- Original Message ----- From: "John Black" <jblack@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, November 25, 2005 12:10 PM
Subject: [pure-silver] Re: [OT] Filmholders, Septums, Total-Disasters





>
Check with Linhof to find out for certain. The U.S.
distributor for Linhof is very knowledible and might answer
the question for you even through you are not here. Ask for
Bob Salomon. HP marketing is at:
http://www.hpmarketingcorp.com/


FWIW, my Linhof TechniKa IVb (6X9) from the late 50s (I think) was supplied
with a GG focusing back withOUT fresnel lens.

JB

I think they supplied both kinds at various times. Its easy enough to check the GG position using a depth micrometer. Remove the back from the camera, the focusing panel is enough. The focusing panel will have a reference surface that contacts the inside back of the camera in the same place that film holders do. Use a flat sheet of metal thick enough not to warp, it must be uniform and flat on both sides and must be large enough to contact all four corners of the panel. Drill a some holes to clear the probe of the depth micrometer. Just at the center is OK but its better to be able to check at the center and corners. Measure its thickness with the micrometer so you can subtract it from the readings. Then lay it on the back and check the distance to the GG surface. The standard distance is 0.190 inches. If there is supposed to be something else there it will be significantly off. I don't know the exact thickness of the Fresnel used by Linhof but they are typically around 1/16th inch or maybe 1 mm in thickness. This is a major error in position for the GG so it will be pretty obvious.
The reason for having a test block that contacts all four corners of the ground glass panel is that most GG panels contact the camera back only at the corners. This leaves an air gap around the GG to vent the bellows when focusing or folding the camera.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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