My Pentax M-Conversion is now almost complete.
Thank you for your inspiration and advice, Roland!
First I modified a KIPON Pentax K-Mount to Leica M-Mount adaptor to show the 50 mm frame in the Rangefinder of a Leica M.
IMG_4731 von
thomas.78 auf Flickr
After unscrewing the last element I thinned down the brass tube with a lathe to fit the "step" of the ring holding the last element:
DSCF3812 von
thomas.78 auf Flickr
Then the brass tube was glued to the ring of the last element, sawn to the calculated lenght + 0.2 mm and then I used emery paper to trim the tube down until the rangefinder at my Berra R3A matches at infinity.
IMG_4834 von
thomas.78 auf Flickr
With the KIPON adapter:
IMG_4833 von
thomas.78 auf Flickr
Together with my Bessa R3A:
IMG_4831 von
thomas.78 auf Flickr
I did some test shots both at ininity and 1 m distance.
The resolution at infinity is ok.
If I do scale focusing at 100 cm, I get the focus at about 94 cm at f/1.4.
If I use the rangefinder at a "real" distance of 100 cm it shows me something a bit less than 100 cm at the scale and I get the focus somewhere between 92 and 94 cm.
So it looks as my lens gives me some front focus using it wide open at close distance.
Now I am wondering if I should adjust the coupling tube to give me spot on focus at 1m and f/1.4 as I want to use the lens primary for available light portraits.
The drawback ist that this procedure would shorten the tube and thereby be irreversible....