Here is how I easily shim the Leitax mounts for Canon:

The correct spacing depends of the particular lens, it is possible that there will be no need of spacing at all.

To check it, I take a series of pictures of a very distant object that has fine detail ( I use an electricity tower).
First picture with the focus ring at hard stop on infinity position, and 3-4 more pictures rotating back the focus ring just a little bit each time.
Checking the results:
---If the first one is out of focus and the focus is improving on the other pictures, this means there is need of shimming, we need more shimming if the good one is the 4th picture than if it is the 2nd. one (for example)
--- If the first one is in focus and the rest are increasingly worst, then the lens and adapter are ok.
---If none of the pictures is in focus and increasingly worst, then the lens is default or the bayonet too thick (very unlikely on a Leitax mount)

The stickers that I use for the postal shipping can have another interesting utility.

I cut pieces of the waxed paper alone and together with the sticker  too.

The waxed paper alone is 0.04mm thick.

Two pieces of waxed paper make 0.08mm.

And the sticker together with the waxed paper measures 0.12mm.

After several trials, I find the necessary thickness.

We have to put many pieces avoiding the screw holes of course.

Now just install the Leitax mount on top of the original Leica-R mount.

And screw it, as you can see, this lens is the Leica-R Aspherical 21-35 Zoom.

This one uses the ten holes Leitax mount, and four of the special thinner screws.
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