[Leica] Re: Hexar Back focus

[Cummer Family <cummer@asiaonline.net>]

Dear Luggers,
I was playing with my Hexar RF today - checking out the film gate where the
half circle is cut which lets us determine that a negative has been shot
with the camera - a neat idea - and my finger slipped off the shutter
button and the closing shutter brushed my thumb. This minor violation of
the shutter - no visible damage - locked the camera up with screen on the
top cover blinking "20" "20" as an error message. I took the batteries out
and reloaded them and the blinking "20 20" remained. So, I hopped the MTR
and rode the subway to Wanchai and the Hexar repair office, which is at
ground level in the back of a Konica film lab on Harbour Drive. The
technician, the affable Mr. Leung, came out and examined the camera. He too
took out the batteries and reinserted them and then he held down the
shutter button for a few seconds and the "20" disappeared from the screen,
the shutter wound, and the camera was restored. Mr. Leung volunteered to
look at the accuracy of infinity focussing even before I asked him and went
outside to look at the rooftop antenna of a far building. He installed his
own Hexar 50mm F2.0 lens and the range finder (as he must have suspected)
focussed slightly beyond infinity. We also tried it with my Voigtlander
Nokton 50mm F1.5, which I knew already focussed beyond infinity. Mr. Leung
said it would take him just a few minutes to correct the focus. He lifted
the exposure compensation dial, undid the top plate screws and lifted the
top plate from the body. He used an apparatus like an oscilloscope without
the cathode ray tube to focus the lens and then turned a single screw in
the top of the rangefinder housing until satisfied. Then he sat the camera
on another machine with the back open and the lens on and shone a light
through the microscope like machine to determine that the lens focussed on
the back plate. Then we went outside and tested both the Hexar lens and the
voigtlander for infinity. Both reached infinity in coincidence of the
rangefinder reaching infinity. This was all done in a very professional
half an hour and a lot less formally than what goes on at the Leica agent.
I asked Mr. Leung to look at the Hexar service manual and read with my own
eyes that the back focus is 28mm +/- 0.03mm - not the 0.06mm which Erwin
reported on May 9 2001 to the LUG:
>From: Erwin Puts  9 May 2001
>Subject: [Leica] Konica facts
>There has been much discussion about the compatibility of Leica lenses
with the Hexar RF body. Most >people, including all of the magazine writers
have assumed that the study of the bayonet mount (that is >does 
>the Leica lens fit onto the Hexar bayonet) is sufficient to declare that
lenses and bodies can be safely >intermixed. Problems have been encountered
and have been discussed as tolerance issues. As far as I 
>know, no one has extended the analysis to the most crucial part: the back
focus or the distance from >bayonet flange to film plane. After measuring
it and checking with the Konica people a most surprising >fact emerges.
>The back focus of the Hexar RF is 28.00mm with a tolerance bandwidth of
0.06mm!
>The Leica data are: 27.80mm with a max tolerance of 0.02mm.The first
observation is this. Leica >tolerances are 3 times as narrow as the Konica
ones (0.02 versus 0.06). Wonder why the Leica is >expensive? This small
difference in tolerance is a hefty task in production engineering.>
I only wish here to set the record straight and have no wish to start
another Leica / Hexar war. I can only report what many Hexar users know,
that in my experience the Hexar takes Leica lenses and focuses them
perfectly adequately - despite the difference in back focus. Like they said
in "Shakespeare in Love" - "It's a mystery!" To be fair, since I don't know
if Erwin is still on the LUG, I have sent the information about what I have
read in the Hexar service manual to him privately.
Cheers
Howard.