6-bit coding and Auto Lens Detection

[jaapv]

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In order to automatically recognize a lens on an M camera, it must have BOTH the correct 6-bit code AND the correct framelines. In fact, Leica implemented it this way to accommodate the Tri-Elmar. For other lenses this is redundant. If you should miscode a lens to an incorrect frameline, it will not be recognized. 

[lct]

1 hour ago, jaapv said:

In order to automatically recognize a lens on an M camera, it must have BOTH the correct 6-bit code AND the correct framelines. In fact, Leica implemented it this way to accommodate the Tri-Elmar. For other lenses this is redundant. If you should miscode a lens to an incorrect frameline, it will not be recognized. 

I don't know with other cameras  but it is not my experience with the M11 i must say. Once tried it with a Skopar 50/2.5. Pen coding it as a Summilux 35/1.4 made the camera recognize it as said Summilux 35 in spite of framelines being 50/75. Then, in case of conflict between 6-bit code and framelines, the 6-bit code seems to be the winner, in this case at least. Other experiences?

[jaapv]

I’m happy to stand corrected or maybe droop this requirement on their later cameras, after all the MATE is pretty vintage by now and I stopped pouring money into the M Austen with the M9. 

[Alexander108]

AFAIK the framelines are mechanically moved. Once you attach the lens you see the lever moving if it's not the default lever position. The 6 bit is for JPG corrections and set the lens EXIF information. Not sure if it has an effect on DNG. 

[beewee]

The reason I mentioned frame line position earlier for the L adapter M is because someone had brought up the idea that, perhaps the frame line selection could act as a 7th bit of information. Technically, the 3 frame line positions could represent 1.5 bits of information.

Currently with 6-bits, there are up to 64 lenses that can be encoded. However, if frame line position could be used, it would raise the theoretical limit to around 180.

[kiwidad]

On 9/14/2025 at 6:38 PM, jaapv said:

The WATE does not differentiate between frameline position as there are no framelines for its focal lengths. It is designed to need only one set of optical corrections, making it behave like a prime lens. The MATE does indeed use the frameline input for the digital pipeline. 

The MATE however does!

in an earlier comment there was mention of 6bit priority over framelines. I think this is not quite correct. I think there is frameline sensing before the lever. Any one pull a digital m apart to see it there is any sensing on the frameline control? If there isn’t how does it differentiate focal length on the MATE.

[jaapv]

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By shifting the bayonet extension on the lens that toggles the framelines on the flange. No need to pull anything apart.

[misteracng]

The MATE is a special case. For digital M camera it reads the 6 bit code so it knows its a MATE, then when you change the focal length on the lens, the frameline switch is moved so the camera knows what position the frameline selector is. This is really specific to the MATE because this is the only lens that mechanically changes the frameline flange on the lens mount. On the SL cameras this is not possible so it only knows the MATE is attached, but not what focal length you are using. The WATE would be different as well, the camera will recognize the lens but you must pick the focal length because it has no frameline adjustment. THis is one of the main reasons they stopped making the MATE. The mechanism is very complex and expensive produce.

[misteracng]

On 9/29/2025 at 10:55 AM, lct said:

Interesting thank you, but i don't understand.
• In auto detection mode, with my uncoded MATE, the M11 says "Uncoded" and exif data say "Focal Length: 0.0 mm" at the 3 lever positions.
• In manual detection mode, the M11 prompts to choose 28mm, 35mm or 50mm. So, when choosing 50mm for instance, the camera says "4/50mm" and exif data say "Focal Length: 50.0 mm" at the 3 lever positions.
• Therefore, in both auto and manual detection modes, the lever positions play no role at all on lens recognition. What i don't understand is how the same lever positions can have suddenly a role on lens recognition when the lens is 6-bit coded, given that there is one code only painted on the flange of the lens.

The m11 does detect the position of the frame line lever, but if the lens is uncoded, moving the lever will not do anything, only the MATE has more then one focal length and frame line selector change. However having frame line detection does allow Leica to have for 6 bit lens combinations. So you could have lenses with the same 6 bit but different frame lines. I think the camera detects 6 bit first then goes to the frameline. I’m not sure I encountered this yet on my SL with the adapter, but if there is more then one lens with the same 6 bit the adapter will not know, it will ask you to select which lens you are using.

[lct]

4 minutes ago, misteracng said:

The m11 does detect the position of the frame line lever, but if the lens is uncoded, moving the lever will not do anything, only the MATE has more then one focal length and frame line selector change. However having frame line detection does allow Leica to have for 6 bit lens combinations. So you could have lenses with the same 6 bit but different frame lines. I think the camera detects 6 bit first then goes to the frameline. I’m not sure I encountered this yet on my SL with the adapter, but if there is more then one lens with the same 6 bit the adapter will not know, it will ask you to select which lens you are using.

Thank you much but i still fail to understand how the simple fact for the lens to be coded can suffice for the camera to take the frameline position into account while this does not happen when the lens is uncoded. I will have to have my MATE coded to understand this i suppose.

[marchyman]

3 hours ago, misteracng said:

The m11 does detect the position of the frame line lever, but if the lens is uncoded, moving the lever will not do anything

Which uncoded lens?  With my uncoded C-biogon 35mm mounted moving the lever shows me alternative frame lines.

 

[jaapv]

4 hours ago, misteracng said:

The m11 does detect the position of the frame line lever, but if the lens is uncoded, moving the lever will not do anything, only the MATE has more then one focal length and frame line selector change. However having frame line detection does allow Leica to have for 6 bit lens combinations. So you could have lenses with the same 6 bit but different frame lines. I think the camera detects 6 bit first then goes to the frameline. I’m not sure I encountered this yet on my SL with the adapter, but if there is more then one lens with the same 6 bit the adapter will not know, it will ask you to select which lens you are using.

Please explain how the optical/digital lens recognition by the code can have any impact on the purely mechanical movement of the framelines. Yes, there is LED involved but that is no more than a light bulb. 

[misteracng]

4 hours ago, jaapv said:

Please explain how the optical/digital lens recognition by the code can have any impact on the purely mechanical movement of the framelines. Yes, there is LED involved but that is no more than a light bulb. 

When the frameline switch is engaged in the mount, the digital M cameras senses that position and the camera knows which position it is in. This of course is not the case for the film M cameras. So when a 6 bit lens is mounted, it also sees which frame line is selected. This allows the same 6 bit code to be used for up to 3 lenses and the camera can tell them apart. Obviously in this case the same 6 bit code cannot be used for say a 28mm and a 90mm because it uses the same frameline set. 

[misteracng]

4 hours ago, marchyman said:

Which uncoded lens?  With my uncoded C-biogon 35mm mounted moving the lever shows me alternative frame lines.

 

Yes the frameline is always selected properly and you can move the lever. I was only referring the lens detection. If there is no 6 bit code, you can change frame lines but the camera is not going to recognize the lens because there is no 6 bit code to start with. It looks at 6 bit code first and if it’s valid then it looks at frameline position to know what lens it is. This may be the reason why brand new released lenses may not be detected until a firmware update and the new code is loaded into the camera.

[jaapv]

Why should a frameline posit

4 minutes ago, misteracng said:

When the frameline switch is engaged in the mount, the digital M cameras senses that position and the camera knows which position it is in. This of course is not the case for the film M cameras. So when a 6 bit lens is mounted, it also sees which frame line is selected. This allows the same 6 bit code to be used for up to 3 lenses and the camera can tell them apart. Obviously in this case the same 6 bit code cannot be used for say a 28mm and a 90mm because it uses the same frameline set. 

The 6-bit code does not even exist for film M cameras - and why should an SL be involved in this (as in your post before) - that camera has nothing to do with framelines. 

[misteracng]

Just now, jaapv said:

Why should a frameline posit

The 6-bit code does not even exist for film M cameras - and why should an SL be involved in this (as in your post before) - that camera has nothing to do with framelines. 

That is correct, on the SL cameras with the Leica adapter, if more then one lens is using the same code, you will be presented the option to select which lens you have because there is no frameline selector, thus the SL cannot tell which lens it is. This happens on the MATE for example. In mounting the lens on the SL2 if automatically brings up the 28/35/50 tri-elmar and you need to select which focal length you are using

[kiwidad]

On 9/30/2025 at 12:30 PM, jaapv said:

By shifting the bayonet extension on the lens that toggles the framelines on the flange. No need to pull anything apart.

However, there has to be electronic detection of the frame lines or the camera would not know focal length of your MATE

[jdlaing]

4 minutes ago, kiwidad said:

However, there has to be electronic detection of the frame lines or the camera would not know focal length of your MATE

No. It’s mechanical. The lens mount has a part that moves when you change focal lengths on an M body. On an SL you choose from a menu.

Edited Wednesday at 11:55 PM by jdlaing

[jaapv]

34 minutes ago, kiwidad said:

However, there has to be electronic detection of the frame lines or the camera would not know focal length of your MATE

The MATE shifts framelines on mechanical M cameras as well. It is completely mechanical by pushing a toggle inside the flange  . The framelines are projected into the viewfinder by sliding metal masks, and a prism illuminated by either the little window or on later digital M cameras a  LED. However digital M cameras have a couple of switches to determine the position of the framelines. Misteragnc is referring to the possibility of using the frameline position as an extra input in lens recognition but Leica would never do that for reasons of retro comparability on older digital M cameras and compatability with L mount adaptation. 

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[lct]

Frameline selection is purely mechanical, including on the MATE, there is no doubt about that. Now, the problem is not frameline selection but lens detection. Does lens detection depend on the  selected frameline, and if yes, how does it work?

Edited Thursday at 12:22 AM by lct