Mixing coded and uncoded lenses - and why does my M8 recognize my uncoded lens?

[nhabedi]

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I understand that 6-bit coding of lenses is only really necessary for wide-angle lenses and as I almost always shoot black-and-white and without filters the corrections applied by the camera and/or the RAW converter aren't much of an issue for me. Still, I thought it would be nice to have lens data available in the files if the lens is known. Unfortunately, it turns out that I'm too oblivious to remember to switch lens recognition on or off depending on the lens I use. Bummer...

 

So, I think I remember that someone on this forum said it wouldn't matter to mix encoded and unencoded lenses. I can't find that posting right now but the statement kind of makes sense to me as an unencoded lens effectively has the "code" 000000 which Leica obviously must have reserved for "unknown lens". That would be ideal for me as my only encoded lens is a 28mm Elmarit while the unencoded lenses are longer (35mm and 50mm).

 

I forgot about these issues for some time as I was busy shooting, but this morning I did a very simple "experiment" and switched lens recognition on on my M8.2 and did some test shots with all three lenses - the 28mm which is recent and 6-bit encoded, a 35mm Summicron from 1991 which is not encoded and an even older 50mm Summicron which also isn't encoded. When I opened the files in Lightroom, the Elmarit shots had "Focal Length: 28mm" in the EXIF data as expected while the 50mm shots had no "Focal Length" field at all, also as expected. Surprisingly, the photos taken with the 35mm lens had "Focal Length: 35mm" fields in the EXIF data although the lens definitely isn't encoded. Huh? What's going on here?

 

Questions:

 

• Am I right to assume that it is safe to always leave lens recognition switched on even if using unencoded lenses or is anyone aware of any problems here? (Leaving aside for a moment "exotic" lenses which might have screws or whatever in the place where the coding should be. I only have the three lenses mentioned.)
   
  
• Any idea why the 35mm Summicron is "recognized"? Has anyone else seen this before? (And if so, is the behaviour consistent? I haven't done enough tests yet to confirm this.) If this is an "accident", it would likely mean that the answer to the first question is "no". If this is by design, I'd be interested to learn how on earth the camera figured out which lens I was using.
  

 

Thanks,

Edi.

[nhabedi]

One more question that just occured to me: Does the M8 actually apply any correction to the DNGs in the camera or is all of this done in C1 or LR using the vendor-supplied profiles? (I probably read that somewhere already, but I forgot. Sorry, I'm getting old...)

 

I'm asking because if the correction isn't applied in-camera, then I would try to hack some kind of "import filter" which applies the correct EXIF data to my files before I import them into Lightroom. In my case it would be easy - if the focal length is 28 mm, there's nothing to do, if it's 35 mm it's the 35 mm Summicron, if there's no focal length, it must be the old 50 mm Summicron...

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[Shootist]

It is being seen by the camera because there is a screw head in the right place.

Question is is it being seen as a 35mm lens with f/2 aperture. Most all older lenses have the same screw pattern on the mount and most are seen as a 90mm f/2.8, at least that has been my experience.

[nhabedi]

It is being seen by the camera because there is a screw head in the right place.

Question is is it being seen as a 35mm lens with f/2 aperture. Most all older lenses have the same screw pattern on the mount and most are seen as a 90mm f/2.8, at least that has been my experience.

 

Ah, OK that makes sense. I looked at the lens and there is indeed a screw head in the area where the codes on the Elmarit are. I would think that the sensor can only mistake one screw for one or two adjacent 1 bits, i.e. only a few bit patters would make sense. For the 90mm f/2.8 you mentioned there's 100110 and 000100, so if the M8 thinks that an uncoded lens is 90mm f/2.8, then my bet would be it thinks it's the Tele-Elmarit (000100). Likewise, the list of lens codes lists 000110 and 011110 for 35mm and I seriously doubt that one screw could be mistaken for four 1 bits, so most likely 000110 is it which matches my lens perfectly...

 

I'll have to actually check the binary files to confirm this, but I'll have to postpone this as I don't have the time now.

 

Still, even if the M8 "identified" my 35mm lens as the wrong one (Summarit, Summilux, whatever), with my minimal setup of three lenses I would have enough info to automatically modify the EXIF data.

 

Thanks for the hint,

Edi.

[ho_co]

One more question that just occured to me: Does the M8 actually apply any correction to the DNGs in the camera or is all of this done in C1 or LR using the vendor-supplied profiles?

The M8 does the correction on-board.

 

The file is exported ready for any raw converter with or without profiles.