Adjusting rangefinder cam for precise focusing

Leica M8 first problem that apperead to me was backfocus on shorter and shorter focusing distances, I mean infinity focus is perfect, short distance focus is made behind the point you adjust the rangefinder for. I tested M8 with 3 lenses 35mm f2 + 50 noct + 75 f1.4 : all 3 lenses did backfocus on short distance with perfect focus on infinity.

I could solve this "easily" (I did it a long time ago with M4-P wich had vert. misaligned RF + front focused RF). Here is how, but be careful, this operation can normaly only be made by a certified Leica reparator. If you do it, it is at your own risk. You could probably loose your waranty with such an operation, or even worse, damage your camera.

Bakfocus on short distance comes from a too short focus sensor lever. To adjust it :

0. before making any adjustement to the RF be sure that your lense(s) focuses perfectly on infinity (very easy to test with a digital camera : 1. put the lens to the stop on infinity, whatever rangefinder is indicating, 2. take a picture of an object very very far away, 3. check sharpness - result should be perfect). Problem in focusing precision could come from a lens whose RF barrel is not properly adjusted for infinity. I have got this happening with a Summilux 75mm.

1. loosen just a little bit the screw which secures the lever on its shaft with a screwdriver (I modified a normal screwdriver to be oblique, so that it fits better the screw at an angle)

2. Turn the ring surrounding the screw by a little amount in the screwing direction, so that the lever is moved to the left.

3. Tighten center screw.

4. The effect of changing lever length is that it changes the angle of the arm with the RF lens barrel and so changes lightly infinity RF position. That's why there is a screw (allen) in the center of the focusing wheel. Adjust it to get a perfect RF infinity.

5. You are ready to make new tests. If it's not OK you can repeat above steps.

The amount of "move" of the lever depands of the amount of backfocusing. The best is to go with very little paths until you reach the perfect focus.

Again, this procedure is a micro-mechanics operation. Don't go in this procedure if you are not familiar with micro-mechanics, and just send camera + lenses to Leica for precise adjustment.