A recent long and winding thread about focusing issues with the Chamonix 4x5 got me to take a closer look at mine. I'm fortunate to own a precision machine shop, and so I have the inspection equipment to measure these things accurately. When I went to remove the glass and fresnel, I noticed that the ground glass was resting on the fresnel, and not actually resting on the narrow steps in the wooden back made to accept the glass. This is because the plastic fresnel is thicker than the recess in the wood that is to contain it. Although the angle of view in the pic here does not show this discrepancy, it does show the corners in question. The GG (top layer) is resting on the plastic lens under it, and not contacting the ledge in the wood it is supposed be against. I measured two film holders (with film in them), a Toyo and a Fidelity, and they were within .003" of each other and the specification, which I believe is 5mm (.197"). On the camera back, the distance to the wood step for the glass measured the same. The camera was made well! My fresnel is lifting the glass about .010" above it's proper location. I need to find a thinner fresnel, or carefully mill or file the edges thinner to allow the glass to seat. If you have a gauge you can measure the step from the fresnel to the outer wood ledge. The wood should be even or higher than the plastic. This post and my suggestion is not intended for the non-technical oriented camera owner.
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