[Leica] Rangefinder error on M9

[hlritter at bex.net (Howard Ritter)]

I have just discovered that the RF on my M9 does not bring the 90 ASPH to 
focus in at least the middle range, specifically 7 meters, although it does 
so, as far as I've been able to tell, at infinity. I have not tested it 
thoroughly at closer range, but I'll do so tomorrow during daylight when I 
can use a low ISO.

I had seen comments on LUG/MUG along these lines previously but not paid 
attention because I didn't yet have an M9. I recall seeing something about 
lenses needing modding in order to focus properly on the M8 or M9, but can't 
recall details.

This is very counterintuitive and perplexing to me. Given that the 
flange-to-sensor distance on digital Ms is the same as the flange-to-film 
distance on analog Ms, how does the problem arise at all, and why does a 
modification of the lens or adjustment of the RF mechanism to accomodate one 
combination not affect the modified unit's performance with other 
combinations?

Any insight or advice would be highly appreciated.

?howard