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

  • From: "John Black" <jblack@xxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Mon, 28 Nov 2005 15:03:08 -0500

> >
>    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.
>

Thank you very much for the good information on checking depth and
distances.  My Linhof is now at Ken Ruth's getting it's sesquicentennial
cleaning and adjustment.  He may check the tolerances on the backs and he
will have to replace the GG in the focusing back as it is broken.

Does anyone on the list know where (other than ebay) I might find 1 or 2 6X9
backs for this Linhof?  I see 6X9 backs all the time on ebay but they are
for the rollfilm back for the 4X5 Linhof Technika. I don't think they are
interchangeable.

JB



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