6-bit lens

[Scott A.]

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For a 35mm Summicron, is 6-bit preferred? Educate me, please. 

[lct]

14 minutes ago, Scott A. said:

For a 35mm Summicron, is 6-bit preferred? Educate me, please. 

Done by Leica yes because Leica will calibrate the lens for digital. That is what Leica did with my own lenses at least but you may wish to check the real work they will do. BTW such calibration can be needed to focus the lens accurately because it has been designed with film in mind, not digital.

[UliWer]

If you don‘t use an M8, you can manually select the proper or an adaequate lens correction from the menue if your lens is uncoded, which has the same purpose as the 6-bit code. With the M10 the electronic correction for lenses is negligable, may be more important for the M9 or M (Typ 240).

[hanexp]

18 minutes ago, lct said:

Done by Leica yes because Leica will calibrate the lens for digital. That is what Leica did with my own lenses at least but you may wish to check the real work they will do. BTW such calibration can be needed to focus the lens accurately because it has been designed with film in mind, not digital.

Besides changing out the rear flange to communicate the lens data to the camera body, what is actually done to calibrate the lens for digital? 

[jaapv]

Film era lenses were constructed to a wider tolerance as film is more forgiving of focus errors. Leica checks ( and if needed corrects) whether a lens is within present-day tolerance.

[adan]

5 hours ago, Scott A. said:

For a 35mm Summicron, is 6-bit preferred? Educate me, please. 

6-bit coding is definitely preferred for M lenses that will be used on digital Leica cameras. Especially for shorter focal lengths (i.e. 35mm-16mm), for reasons of color-vignetting issues with those wide-angle views on digital sensors. Images made with those wide lenses can show color stains that are hard to correct manually - but are corrected automatically and seamlessly at the moment of exposure IF the camera can sense what lens is in use via the 6-bit code.

But also for longer lenses, if one wants the camera to record the lens used in the image EXIF metadata, for recall in computer editing and cataloging software. That is, a 35mm Summicron ASPH with 6-bit coding will be tagged in the metadata as "35mm Summicron-M ASPH f/2.0," while an earlier copy of the same lens without coding will be tagged only as "-------- f/1.0." Or on the M10, possibly as some other lens altogether.

For lenses that will be used only on film Leicas (M3-M7, MP, M-A) - or on other camera brands (e.g. Sony, Fuji, etc.) - there is no particular value to 6-bit coding. It will serve no function.

As of today, to have 6-bit coding added to a lens by Leica costs about US $300. Thus used lenses with coding already in place usually run $200-300 more than uncoded legacy lenses of the same type (although that depends on overall condition otherwise, as usual).

[M11 for me]

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vor 5 Stunden schrieb jaapv:

Film era lenses were constructed to a wider tolerance as film is more forgiving of focus errors. Leica checks ( and if needed corrects) whether a lens is within present-day tolerance.

Could you pls explain what you mean exactly? I do not understand how focusing error (tolerance) could be corrected by means of a code on the lens.

[250swb]

1 hour ago, M10 for me said:

Could you pls explain what you mean exactly? I do not understand how focusing error (tolerance) could be corrected by means of a code on the lens.

At what point in Jaap's reply did he use the word 'code'? What he said is perfectly clear.

[jaapv]

2 hours ago, M10 for me said:

Could you pls explain what you mean exactly? I do not understand how focusing error (tolerance) could be corrected by means of a code on the lens.

Actually Leica doesn't code the lens, they replace the mount with a coded one. As a separate service they check whether the lens is within tolerance. if not, they take it apart and adjust it, using the shims incorporated in the design for the purpose.

[jaapv]

1 hour ago, 250swb said:

At what point in Jaap's reply did he use the word 'code'? What he said is perfectly clear.

Although the grammar is a bit lame...

[M11 for me]

vor 2 Stunden schrieb jaapv:

Actually Leica doesn't code the lens, they replace the mount with a coded one. As a separate service they check whether the lens is within tolerance. if not, they take it apart and adjust it, using the shims incorporated in the design for the purpose.

Oh, I fully misunderstood then. Thanks for clarifying.

[M11 for me]

vor 4 Stunden schrieb 250swb:

At what point in Jaap's reply did he use the word 'code'? What he said is perfectly clear.

To me it was not clear. Very good that you understood. Brains work differently. Mine is very slow. 

[lct]

6 hours ago, adan said:

6-bit coding is definitely preferred for M lenses that will be used on digital Leica cameras. Especially for shorter focal lengths (i.e. 35mm-16mm), for reasons of color-vignetting issues with those wide-angle views on digital sensors. [...]

Also to correct distortion from 16mm to 35mm M lenses on the digital CL but apparently not on the M240 i don't know why.

Edited January 2, 2020 by lct

[a5m]

10 hours ago, adan said:

if one wants the camera to record the lens used in the image EXIF metadata, for recall in computer editing and cataloging software. That is, a 35mm Summicron ASPH with 6-bit coding will be tagged in the metadata as "35mm Summicron-M ASPH f/2.0," while an earlier copy of the same lens without coding will be tagged only as "-------- f/1.0." Or on the M10, possibly as some other lens altogether.

Just wanted to add that you can also manually select the lens in the camera's menu if it is not 6-Bit Coded and get the correct EXIF metadata.

[hanexp]

9 hours ago, jaapv said:

As a separate service they check whether the lens is within tolerance. if not, they take it apart and adjust it, using the shims incorporated in the design for the purpose.

Thank you for clarifying your initial comment. Very helpdful

[Scott A.]

Thanks for the replies, they’ve been very helpful.