How to adjust Infinity stop for 9x12 plate cameras

Hi

I have two 9x12 plate cameras that the infinity stop is not correct, according to ground glass image.
I cannot seem to find an easy way to adjust them. They are off by 3-5mm, so shimming the lens will be very awkward.
Do you have any suggestions? Thanks!

The Zeiss Ikon Maximar 207/7: there is no adjustment possible for the distance scale




The Voigtlander Avus: there is small adjustment possible for distance scale, but not enough

I'd want a lot of evidence that Zeiss Ikon were wrong and I was right, before making any change to my camera. I'd check no previous owner has disturbed the lens and left it at a different position; and that the camera has the lens it should have; and the front and rear groups both belong to the same lens.
Also, I'd try to check that the ground glass belongs to this camera and that it sits where it should be; turning the glass over in its frame would leave the matte surface a couple of mm out.

Dustin McAmera said:

turning the glass over in its frame would leave the matte surface a couple of mm out.

Click to expand...

To expand on this, the matte side of the focusing screen should be toward the lens.

Also, is the camera focusing too close (i.e. you can focus beyond, say, 20 feet), or does it go "past infinity", with infinity focus coming before the standard reaches the stop? The latter is strong evidence the lens has been either replaced or the spacing between front and rear groups is wrong; the former may indicate the front element (of the two in the front group) is too far from the second element (Tessar type and triplet lenses can be focused by unscrewing the front element from the front cell).

The Zeiss Maximar comes from a collector, and I don't find any evidence of tampering. Everything looks original, including the lens, the ground glass and focusing hood.

The Voigtlander Avus, on the other hand, I have to take off the lens to service the shutter. But it was off before I took off the lens. And I believe I installed everything back snugly and logically. And its ground glass and focus hood is original fit.

For both cameras, they focus too close when set at infinity stop. Instead of infinity, they focus at around 15ft.

Thus I'm a bit perplexed.

Okay, that indicates that either the front standard's lock to the bed, or the bed's focusing rail minimum position is too far from the film plane (by several millimeters). I presume you've ensured the focusing tray is fully retracted. I've seen felt or hard shims between shutter and front standard on some plate cameras when I've had the shutter off; that would be a lot of shim and produce a visible space behind the shutter and you'd surely be aware of it, having had the lenses (and presumably shutters) off. Is it possible the collector who had them before you might have swapped lens cells for cosmetic reasons, with no expectation of ever actually shooting with the cameras? If front and rear cells aren't matched as originals, it's possible for the focal length to change.

Alternately, that amount of focus change is less than a millimeter change in depth of the first element away from the second in Tessar type and triplet lenses. If someone before you had the individual glass elements out of the cells for cleaning, and missed a fraction of a turn returning the front element, you'd have your fifteen feet. You might even get that if the second element is in backward.