JM coded CV 15mm strange behavior

[gmaurizio]

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Dear friends,

I have a nice collection of JM adapter coded for some of my CV lenses. They all work fine, using white and black enamel and taking consideration there are no light leaks. Some of them I use with uv/ir filters, others do not need it [always at least].

My CV 15mm is showing a weird behavior. When I use it with Lens detection + uv/ir filter, it correctly brings up the WATE menu, I do select 16mm, and the pictures happily show the 16mm lens on the EXIF. So far, nothing wrong.

When I switch to just lens detection, in order to keep the default 16mm set and without the filter, both the INFO screen and the DNG do not show any lens...????!!!????

 

Does anyone have a clue?

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[delander †]

Gus,

 

I think this is normal behaviour for the WATE when IR/UV is not selected with the latest firmware 1.107

 

Jeff

[ho_co]

Gus--

Jeff is correct. It would make no sense to assign a 'default focal length' for a WATE, since there are two chances in three that it would be wrong. Your camera and adapter are behaving correctly.

 

--HC

[sean_reid]

Its normal and the WATE behaves in the same way.

 

Cheers,

 

Sean

[gmaurizio]

Jrff, Howard and Sean, thanks so much!!!

While it makes the WATE and therefore the CV15mm behave different from the other lenses when code detection is on, I accept your knowledge. I wonder why Leica choose to ignore that particular lens, when it does not have a filter, in the EXIF and vignetting corrections..??

 

Thanks and now I can indeed go to sleep without concerns

[ho_co]

Gus--

Sleep peacefully! The story is more complex than you might expect.

 

When the M8 and the WATE were designed, no one knew about the IR problem. The lens was designed so that the vignetting correction was the same for all three focal lengths, and unlike the Tri-Elmar 28-35-50, which automatically changes the frame lines and changes its focal length in the EXIF data, the lens didn't signal the camera what focal length had been set. (After all, the camera didn't have framelines for these focal lengths anyway.) At that time, the lens ID appeared as 18mm in the EXIF.

 

Then the IR problem was discovered; filters were proposed; cyan drift was discovered. Luckily, the M8 firmware could be modified to accommodate the latter, but that brought about the need for the extra menu setting that required indicating which of the three vignetting corrections it was to apply.

 

So now, when using filters at any rate, the firmware would write the actual focal length into the file. So it became meaningless to leave the default "18mm" entry in the EXIF data when the lens was used without filter.

 

I don't know whether it was necessary to eliminate the "18mm" entry (that is, whether the firmware didn't allow for an instruction like "if nothing else is entered, call it 18mm"), or whether it was a choice. A number of WATE users disliked having the lens always show up as an 18mm when it might have been 16mm or 21mm.

 

So your CV 15 + LT-M8 adapter has inherited all that history.

 

Sleep well; the behavior is just a product of the development of the WATE.

 

--HC

[gmaurizio]

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Howard, now my doubts and concerns have been put down to final rest! Thanks for the thorough explanation.

On a side note, I wonder if the complexity of the WATE will not hunt its owners some years from now.... Probably not. The MATE was discontinued, though...

Thanks guys...

[ho_co]

...I wonder if the complexity of the WATE will not hunt its owners some years from now.... Probably not. The MATE was discontinued, though...

Can't predict the future, of course, but actually the MATE was much more complex:

 

--A bayonet with a section that moved to tell the frame lines which focal length was set. That required a spring to pull it back to rest position, plus the linkages to move it a couple millimeters when the focal length was changed by rotating through about 30 degrees.

 

--A design that required going from 28 to 50 to 35, simply because that's the way the preview frames had been designed from the M3 days; that meant moving parts first forward, then back again, while rotating the lens collar always the same direction.

 

From what I read, the WATE is actually the equivalent of a zoom lens. There are no finder frames to move, and the design is such that it just moves from 16 to 18 to 21 without having to switch direction during rotation of the focal length collar.

 

And then on the other hand there's the CV 15, without even a rangfinder coupling--nothing to do but take pictures.

 

--HC

[jlm]

since the frame selector postion has been identifed as a coding element for the WATE, I wonder if it is also an element for other lenses? since it is three postion, we have 7-1/2 bits!