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135/f3.4 APO M lens 6-bit code question


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Greetings!

 

This question might have been mentioned before, though I have not been into here for a while... 

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It about the current model of 135/f3.4 APO lens.  Mine was a new one obtained just before Leica eventually put the 6-bit code on the 135 f3.4...

 

My question is that would it be worth to go through the trouble to send in the lens to Leica to have the 6-bit code fitted on?   What are the benefits and advantages to have the 6-bit code on this lens, or not much for this 135mm telephone lens?

 

When I got this lens, Leica was saying there was not much point (or can not) put the 6-bit code on the 135 f3.4 lens, however it eventually does put the 6-bit code on it...  

     Edited by yst
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Hi yst. I've got this lens and it came 6bit coded. To be honest I can't see any difference in images taken on my Monochrom if Its set to read the lens code or if I forget and leave the code reader in the camera off. I believe it only marks the exif data on the image and is more important on wide angle lenses for corrections but there may be more knowledgable information out there. Hope this helps. Regards Robin. 

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Yes : the "corrections" applied to a 135mm/taken frame are little significant or even nil... the real usefulness is in recording the EXIF data ; in my opinion , doesn't worth time and expense (even without exif data, it's easy to recognize a picture taken with 135 focal...

 ) Edited by luigi bertolotti
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I like having the focal length coded in the EXIF data and have had two older lenses (90/2 and 21/2.8) 6 bit coded to make the process automatic. Sent to DAG, he did it for less cost, using the same parts, and in less time than Leica NJ would have taken.

Edited by Gregm61
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I have noticed that older lenses, with 6-bit coding added by Leica, often perform somewhat better (focus and clarity). I assume this is simply because Leica does a re-collimation and other checks in the process of handling and disassembling the lens - they don't want a lot of "You serviced my lens and now the focus is off" complaints afterwards. More noticable with tele lenses (90mm TE, 75mm Summilux). Nothing to do with the presence of 6-bit coding per se, however. Just a side-effect of Leica having tuned the lens in the process.

 

Obviously I've seen only a small sample statistically, though.

 

Additionally, Leica has tightened up their tolerances since moving to the new Wetzlar factory, and thus the 135 APOs with built-in 6-bit coding (i.e. very recent) should be, and in my very limited experience are, a bit more precise in focusing.

 

OTOH my 1968 Tele-Elmar 135 f/4, that is not and cannot be 6-bit coded (or had any other service in its 50-year life, that I know of), also focuses quite well.

 

Net- net - if your current uncoded APO-Telyt is already focusing precisely for you, you won't gain that benefit. And as mentioned, the 135s are already so "telecentric" in design (glass a long way from the sensor compared to wide-angles) that there is no need for the image corrections that 6-bit coding provides, just the convenience of EXIF lens data.

________________________

 

Of note, the new M10 has a neat feature whereby if one has only one lens without 6-bit coding, the camera can be set permanently to manual lens ID, and to that lens. If a 6-bit-coded lens is then mounted, the camera automatically senses the 6-bit coding, and reverts to using the 6-bit coding.

 

Works a treat for me - my 135 Tele-Elmar is my only lens without coding, so I've set up Manual lens ID > M lenses > 135 Tele-Elmar, and get that in EXIF using that lens. And if I swap to my coded 21/35/75/90 - they also all show up in EXIF accurately, without having to stop and go into the lens menu.

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Only important if you want the lens detail embedded in your digital images. It's the only form of communication between body and lens.

 

If you just shoot film, it's of no utility at all.

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As Ecar's link shows, 6-bit coding is a set of 6 binary (black is 1, white is 0) engraved and paint-filled marks on the back of the lens mount for such lenses. These are read by an infrared LED/detector device (black slot) on the camera lens mounts of digital M cameras. As Gregm61 says, the coding has no effect, good or bad, on film cameras.

 

http://www.overgaard.dk/thorstenovergaardcom_copyrighted_graphics/1694-Leica-M9-was-ist-das-315w/L1090141_LR6-Process-2010-315w.jpg

 

Their general function is to communicate to the camera the lens focal-length/model that is mounted - analogous to the gold electrical contacts on other camera-makers' lenses: https://picturecorrect-wpengine.netdna-ssl.com/wp-content/uploads/2014/07/dslr-maintenance-8.jpg

 

By reading the 6-bit code, and thus knowing which lens is mounted, the camera "knows" how to do three things:

 

1) name the lens used, in a picture's EXIF metadata, so that you can tell which lens you used in years to come.

2) make corrections for vignetting, due to the different "surface" of a digital sensor compared with film - especially with wideangle Leica M lenses

3) make corrections for color vignetting and stains, due to the different surface of a digital sensor compared with film - especially with wideangle Leica M lenses

4) adjust the "low shutter speed" warning in the viewfinder of digital Leica Ms, depending on focal length (more chance of visible camera shake with a 90mm than a 28mm).

 

Items 2 and 3 are essentially the camera digitally "cleaning up" pictures to eliminate the vignetting and color stains, before it writes the picture data to the SD card, based on knowing, from a stored database, how a particular focal length and era of lens will behave on a digital sensor.

 

http://www.overgaard.dk/thorstenovergaardcom_copyrighted_graphics/uncoded-versus-coded-leica-lens-images-640w.jpg

 

Very important corrections for the wideangle lenses (35mm or wider) - but only marginally useful (as this thread discusses) for lenses 50mm and longer. Very important for shooting color, not as important if the final picture goal is B&W (or using a Monochrom camera).

Edited by adan
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To be perfectly honest I expected something more advanced. Summing up this is just passive lens type description readable by camera body. This is also huge difference between Leica approach and commonly used gold electronic contacts. Also - this gives answer to the question why Leica EXIF doesn't contains information about focus value and aperture. Because there is no way to communicate those data to camera body without single piece of working electronic module. Leica lenses are pure mechanical without even symbolic resistor inside.

 

I my opinion lens physics and optics  are independent from backside media. It should be the same for film and digital sensor. Therefore, also analog photography is influenced by lens profile.

 

I am also not sure which module updates/corrects image basing on lens information? Leica Firmware? If yes - also on RAW (DNG) format or only JPEG? I may also confirm that LR is able to update on visible way DNG M10 image basing on Adobe lenses profiles.

 

6-bit code approach also limits possibility to include lenses type/name in EXIF only to Leica lenses. I own two Voigllander lenses. Of course, there is no way to include information about them in EXIF of my M10 image. However, it is possible to use proper correction profile in Adobe LR. The only problem is that it must be done by hand as both lenses are recognized by camera body as "R-Adaptor M" in automatic lens selection mode.

 

Thank you all for detailed explanations.

 

 

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Not sure if i answer your questions but to begin with, the Leica M lens coding is called "6-bit coding" because six fields in the bayonet ring are marked in black or white to represent a number from 1 to 64 in binary code. The camera reads this information optically and can identify the lens on the basis of this code provided it is consistent with the flange of the lens. A correction will then be applied to the raw and jpeg files by the firmware of the camera.
This way, one can correct pics taken with a CV 21/4 lens for instance by painting the Elmarit 21/2.8’s code (000001) on the flange of the lens. Or without any DIY, by choosing "21 f/2.8 11134" in the lens detection menu of the camera. The exif data of the pic files will then say that the lens is an Elmarit 21/2.8.

 

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1. "Advanced" and "Leica M" are mutually exclusive concepts.

 

More seriously - yes, Leica had to, and wanted to, make their digital cameras as backwards-compatible as possible to lenses designed for film decades ago. They know their customers. So they did not design a system that required chips in the lenses (for how can one fit a chip or a resistor into a 1980 35mm lens designed for film?). Leica will never put electronics into their M lenses (if you want that, buy an S or an SL or a TL). And yes, that means M lenses will never: be auto-focus; transmit aperture used; or transmit the focus setting.

 

2. The "module" that does the important corrections is the camera firmware and the camera's main CPU. For either RAW or JPEG. Additionally - Adobe may provide adjustments for lens distortion, and/or color aberrations, through their software recognizing the passive lens ID.

 

3. I'm glad you have an opinion - but in reality there are very large structural (3D construction) differences between film (a plastic base with a gelatin coating full of silver) and a digital sensor (a 3D "stack" of microlenses, IR filtering, color filters for color photography, and "wells" within each pixel that capture the electrons produced by light). The gelatin in film diffuses light - the structure of a sensor bends light.

 

As it happens, the Leica M wide-angles in particular that 1) sit very close to the sensor/film and 2) are not optically designed for the properties of a digital sensor - produce real problems, exhibited as the color stains in my previous examples on a digital sensor in the current state of the art. The strongly sloping light rays of a Leica 21mm tend to "leak" from the red filter of a red pixel onto a neighboring green pixel, or vice versa, when very close to the image edges. Leica has improved that with newer sesnors - but the problem is not fully eliminated, except by firmware corrections according to the lens in use.

 

http://3.bp.blogspot.com/-LYjEVFqryuU/UFtCrjLCF-I/AAAAAAAACa8/_W_dLr7yCTw/s1600/Leica-24MP-MAX-CMOSIS-sensor.png

 

SLR lenses - by virtue of having to clear a moving mirror - sit much farther away from the sensor/film, and do not not produce the same problems to the same extent. For years Leica said they could not make a digital camea that worked with their existing lenses - eventually the market forced them to come up with a solution (the 6-bit coding) that did not involve obsoleting 50-80 years of existing lenses. (Although even so, a few lenses from the past are simply not reasonably compatable with the current state of digital sensor construction (e.g. 21mm Super-Angulons).

 

Now Leica could have done as Canon did 30 years ago when Canon changed to autofocus - change the whole lens mount and added contacts and so on, leaving their existing Canon FD customers out in the cold ("Sorry, your $$$ collection of lenses will no long even fit on our new cameras"). Leica chose not to do that, as far as the M rangefinder system is concerned.

 

4. As to M lenses made by someone other than Leica (e.g. Voigtlander, Zeiss) - frankly, that is not Leica's problem. They are an optics company in business to sell lenses (for which they provide cameras). They are not in business to sell cameras that take other manufacturer's lenses. As it happens, as lct says, there are some workarounds to use 3rd-party lenses on a digital M, if one must. And - again - it really only matters for wideangle lenses. A Voigtlander 50 or 75 or 90 will function quite well on a digital Leica, without 6-bit coding.

Edited by adan
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My wife got me a shirt that reads "Science doesn't care what you believe".

Sure, have your opinion about physics, physics doesn't care.

As usual, adan did the actual explaining, I just offer a sideline commentary.

Edited by michaelwj
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...Also - this gives answer to the question why Leica EXIF doesn't contains information about focus value and aperture. ...

Indeed the EXIF data of digital M gives an information about aperture... but is just an "estimate"... there is a front sensor which measures the light, and given that camera does know the exposure time used, it can compute (and record) the aperture : I have been always amazed that Leica did introduce an additional component just to provide an information that, many times, is far from trustable (it's lot of time that I even don't take note of it... should it be absent, would be the same for me).

Anyway... let's say that they did something to overcome the intrinsic limitations of their system... M system is what IS and USED TO BE : as pointed by Adan, backwards compatibility is one of the main points that keeps us faithful in the brand...

Edited by luigi bertolotti
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Just for the record - the M10 currently no longer even estimates aperture used. EXIF line for aperture used is "--". Users have complained, so that function may reappear in M10 firmware eventually (the light sensor is still there).

 

It's a two-edged sword - some people complained because the "estimate" was so obviously wrong sometimes - e.g. f/3.5 when you KNOW you used f/2, etc. Different focal lengths mean the external reference sensor is seeing a different light pattern than the internal meter. So Leica will get complaints either way.

 

OTOH - the approximate aperture actually in use is (or was) used in adjusting the CPU corrections for vignetting (since the vignetting pattern changes with aperture - there's more vignetting wide-open than at f/5.6), so the M10 may still be sensing that "for internal use only". Only someone who can read Leica's operating code would know for sure.

Edited by adan
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Just for the record - the M10 currently no longer even estimates aperture used. EXIF line for aperture used is "--". Users have complained, so that function may reappear in M10 firmware eventually (the light sensor is still there).

 

It's a two-edged sword - some people complained because the "estimate" was so obviously wrong sometimes - e.g. f/3.5 when you KNOW you used f/2, etc. Different focal lengths mean the external reference sensor is seeing a different light pattern than the internal meter. So Leica will get complaints either way.

 

OTOH - the approximate aperture actually in use is (or was) used in adjusting the CPU corrections for vignetting (since the vignetting pattern changes with aperture - there's more vignetting wide-open than at f/5.6), so the M10 may still be sensing that "for internal use only". Only someone who can read Leica's operating code would know for sure.

 

Count me in the 'wanna have it back camp'.  I often manually bracket apertures and find it comforting, not to mention educational, for the camera to at least provide a guess as to aperture for each shot.  When I come home, tired after being out for the day with a couple of hundred shots to review, it's often difficult to accurately remember the settings for every particular photograph, not to mention which uncoded lens was used for what (yes I'm too lazy to code them and way too ADD to manually enter the info every time I change a lenses).  I've found, now that I'm shooting with two bodies, a 240 and M10, that its surprising how well just a that one crucial bit of data serves as a little poke up side my aging gray matter.  Its loss is not the end of the world, but in my view it is a loss. Perhaps the solution for folks that are annoyed by its inaccuracy is to allow its inclusion to be configurable.   

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