Dodgy mount registering/not registering 6 bit coding

[lawman]

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[pico]

[...] The mechanical actuator driven by the lens bayonet sets both the frame-lines and the switches, trouble is it doesn't do both exactly simultaneously. Usually close enough but not always.

 

Thank you for the clarification. So, when one switches the Tri-Elmar focal lengths, the cam for frame selection must move, but still be compatible with pre-digital M bodies. Correct? I wonder why Leica chose to use those little switches if existing mechanical means worked. (But I wonder about a lot of things.)

[ModernMan]

Thank you for the clarification. So, when one switches the Tri-Elmar focal lengths, the cam for frame selection must move, but still be compatible with pre-digital M bodies. Correct?

 

Correct. Lens selection "cam" sets the frame lines for the correct focal length for all lenses, including MATE 28-35-50, for all M bodies film and digital.

 

I wonder why Leica chose to use those little switches if existing mechanical means worked. (But I wonder about a lot of things.)

 

The switches are only in digital bodies to let the firmware know the focal length. In the digital bodies the frame lines are still set mechanically (even in the M240 where they are illuminated by LEDs).

[ModernMan]

Resurrecting this thread to add an interesting observation.

 

The other day, I just happened to be looking at a couple of M-lenses under my stereo microscope (Leica of course) and noticed that the shape of the 6-bit coding recesses (“pits”) was very-subtly different on some lenses.   Interestingly, some lenses had rectangular pits (with a slightly pie-shaped space between them), whereas on most lenses the pits are slightly pie-shaped (with a rectangular space between them). Further examination revealed that just the lenses exhibiting the problems discussed in this thread  (newer 50/75mm) had rectangular pits, whereas all the lenses (of 20 or so that I then examined) that work consistently without issue have pie-shaped pits. Well..., how about that?

 

Out of curiosity, I obtained a new 50mm bayonet ring from Leica and it came with the apparently-now-uniformly-standard pie-shaped pits. It works without issue. Updated all my newer 50/75 lenses with new bayonet rings.

 

Photo of rectangular pits which are associated with problematic behavior on the M240. Notice that the space between the pits is slightly pie-shaped:

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Photo of pie-shaped pits which seem to now be the uniform standard from Leica. The difference in shape is very subtle indeed, but unambiguous.

 

Of course, we don't know that its the shape of the pits which causes the issue, just that adapter rings with the rectangular pits demonstrate the issue.

 

 

 

 

[sblutter]

If you're only shooting DNG, just turn lens detection off.   Doesn't do anything anyway, frustration obviated.  I never could find that setting on the M3...

[thedirektor]

My M had to be sent back because of this issue. It's ready to be collected from Mayfair. Took about 2 working weeks. Apparently they've replaces the camera 6-bit reader and the lens coding (I sent the lens too)

 

I may be wrong but perhaps there is actually another problem with the M's that is a manufacturing defect (like the lugs) but they're not issuing a recall until people notice and they will send them back for repair.

 

Also - is it usual they have the relevant part in stock or do they expect a flurry of units to be sent back for repair?

 

May I ask how old your M was and when you started noticing the problem ? My brand new 262 started not recognising the lens almost out the box. Thanks