RE: [Leica] Re: Min. focus accuracy of Leica lenses and the Hexar RF

["Dan Honemann" <ddh@home.com>]

Dante,

> What I found interesting about the test (if it was done
> accurately) is that the
> M6 failed to put the 75 in the same place it put the other two
> lenses.  This is the whole accuracy/precision thing.

I found this of interest as well, and it did so on two separate tests.  I'll
get the results of the third this week.

> Of course, this close-in testing requires that you only turn the
> lens one way
> (usually, from what I understand, you go near to far, but here that breaks
> down).

Not sure what you mean here.  In my tests, I turned the focus ring for each
lens all the way to its nearest focus (i.e., to the point where it wouldn't
turn clockwise any farther) and moved the tripod back and forth until the
images in the rangefinder coincide.  I also drew a bright red line on the
ruler at the 6" mark to give me a better target on which to focus.

The one test I haven't tried is putting the focus ring on the last distance
mark printed on the barrel (e.g., .7m on the 50/2) and following the same
process.  I'll do that today.  It may very well turn out, in the case of the
Hexar RF at least, that the rangefinder will only focus these lenses
accurately to .7m--the rangefinder cam seems to disengage at that point.
That would explain why all three lenses wind up focusing a couple inches
closer than the rangefinder would put them at this nearest distance.

I still wonder what business these lens' focus rings have turning beyond
their listed min. focus capacity, anyway (my 35 and 50 turn closer than .7m
by a quarter inch, and the 75 turns a full half inch beyond the last printed
figure on the lens, which is 2.5 feet).  Perhaps the greater anomaly is not
that the 75 focuses two inches closer than the rangefinder indicates on my
M6, but that the 35 and 50 do manage to focus accurately (in accordance with
the M6 rangefinder) closer than their listed min. distance.

I'll take out the tape measure tonight to see if the distance from the
subject to the film plane is actually closer than .7m once focus is achieved
with the ring turned all the way clockwise--or if the distance marks on the
lens barrel are what's off.  In every case, the focus ring does not turn
beyond the middle of the printed infinity symbol in the other direction (and
both rangefinders seem to have infinity lined up accurately), so this only
affects the short end.

Dan