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6 bit coding m lenses
- Thread starter gooomz
- Start date
douglasf13
New member
Nope, there are 7 or 8 identifications for 50mm lenses alone in the menus. For example, there is a setting that includes all of the 50 Summilux pre-ASPHs, and another for the ASPHs.
Double Negative
Not Available
Lens coding depends on two things:
1) The framelines that the mount of the lens brings up (in this case generally 50/75)
2) The exact Leica Lens Code that's on the mount.
1) The framelines that the mount of the lens brings up (in this case generally 50/75)
2) The exact Leica Lens Code that's on the mount.
douglasf13
New member
Didn't know about the framelines thing. What is the reason for that? Do some lenses use the same code, but it is differentiated by the framelines called up?
Double Negative
Not Available
Yep, for example just with the 50/75 framelines... Give it one code and the lens is a 50. Give it a different code, it's a 75.
6-bit coding started with the M8, and its framelines were... Different - 24-35, 50-75 and 28-90. Also, on focal lengths that didn't have corresponding framelines - they had to bring up something so that was used to differentiate as well. Case in point... Tri-Elmar 18 brought up 28/90. Newest Super-Elmar 18mm brings up 50/75. Plus codes are different!
6-bit coding started with the M8, and its framelines were... Different - 24-35, 50-75 and 28-90. Also, on focal lengths that didn't have corresponding framelines - they had to bring up something so that was used to differentiate as well. Case in point... Tri-Elmar 18 brought up 28/90. Newest Super-Elmar 18mm brings up 50/75. Plus codes are different!
tele_player
New member
I don't see any duplicated 6-bit codes in the list on L-Camera Forum, but the frame selection isn't ignored, either. If you have a coded 50 cron, watch what is displayed in the Info screen while you move the frameline selector to the other two positions. In the 28/90 position, the lens is identified as uncoded. In the 50/75 and 35/135 positions, it shows 50mm f/2.
-Robert
I'm sure Leica did this to increase the number of potential codes, but it does cause issues for some third party lenses. For example the Zeiss wides bring up the 50/75 framelines rather than the 28/90 that Leica uses. This makes it impossible to code a ZM21 as a Leica 21mm with a sharpie without either manually selecting the framline or replacing the mounting flange. ( I believe that I read that Zeiss has changed the framelines for more recent lenses, but worth checking)
Double Negative
Not Available
Exactly. Zeiss offered alternate mount flanges early on; I think they just silently changed them once and for all. I also believe they added the groove to all mounts (to better hold codes without wearing off) while moving screws that were in the coding location on newer lenses.
douglasf13
New member
Interesting, thanks everyone.
FWIW, I've stopped using coding altogether, since I don't like what the vignetting correction does in lowlight. I just the flat field plugin in LR if there is a color shift issue. It works great.
FWIW, I've stopped using coding altogether, since I don't like what the vignetting correction does in lowlight. I just the flat field plugin in LR if there is a color shift issue. It works great.
scott kirkpatrick
Well-known member
Not really. Each 6-bit code indicates one focal length and lens type, and also sets up color corrections (red vignetting, Italian flag effect...) that Leica feels are best for that family. The only exception is the out of production 28-35-50 mm Tri-Elmar, in which the lens mount lug moves when you change focal lengths so that the correct framelines come up. In the M8 days, you could read the firmware in a text editor and see the tables that matched lens group ids with firmware corrections. There are actually 8 bits, six for the black and white lines on the mount, and two for the mount lugs. The firmware tables contain an entry for what the mount lug should be. That's why Zeiss had to change its mounts. If the camera senses the wrong mount lug position, it will not identify the lens.
There's a weird complication. Suppose you push or pull on the frame lever; does the lens identification change or fail? Mark Norton's detailed disassembly showed what is going on. The frame lever is coupled to the mechanism (levers and two microswitches) that recognize the mount lug position through springs. If you push the frame lever towards the lens (from 35 to 50 or 28/90), the switches see this as a change in mount lug position. But if you pull the frame lever away from the lens (from 28/90 to 50 to 35), the microswitches are not affected. This means if you want to override the vignetting corrections for a 6-bit coded lens, you can achieve this by pushing the frame lever. But only if the lever starts in a position where it can be pushed. I think this awkward piece of engineering must have embarrassed Leica, since I see that the frame lever has vanished from the latest models.
scott
Hosermage
Active member
The Zeiss 25mm I used to own brought up the 35/135 frameline on the M9, which would have been correct for M8's 24/35 framelines. Since I was coding it as 28 Elmarit ASPH, I had to use the frame lever. Now the ME removed the lever, does it means it will read correctly regardless of the framelines, or does it make it impossible to correct it without changing the flange?
I believe in LR up in the top panel when you filter lenses it shows which lens you have used. Also at the bottom of the Info area on the right side of LR it shows camera and lens data.
douglasf13
New member
In LR, you can also set the info overlay (that sits in the top left hand corner of your pic) to list the lens in the develop module. Not sure about Aperture.
scott kirkpatrick
Well-known member
I don't have an ME, but I would bet the second outcome, that the complex, spring-loaded linkage to the frame lever is completely gone (saves cost and space) and the frames themselves are rigidly determined by the mount lug position. If someone reading this has a Zeiss 25, it would be nice to know if the firmware subsequent to the M9 has stopped caring about the lug position.
scott