[Leica] IMGS: Tests with MM and M246

[Howard Ritter]

Can anyone explain how Lightroom reports an aperture for images made with M cameras, which don’t have a way to report their aperture setting to the camera? All the camera knows is what the lens’s maximum aperture is, as reported by the 6-bit code or manually.

I just ran off a series of images with a coded 24/2.8, one at each usual stop from 2.8 to 16. LR reports the apertures as 2.8, 3.4, 4.8, 6.8, 9.5, and 13. The aperture could be inferred from the integrated light intensity, but only if the camera knows the intensity of the illumination of the subject, which of course it doesn’t. I’m puzzled not only by the fact that LR reports an aperture setting, which the camera has no means of knowing, but even more by the fact that the values are different for each exposure, increasing continuously in the right direction, and most of all by the fact that the values are, as Tina says, in the ball park. And the Mac’s Preview app reports an Aperture Value, which for the same sequence of images also increases correctly, but ranges from 2.97 to 7.4. 

With a non-coded 35/1.4 and lens data entered manually, LR reports the apertures as 1.4, 2, 2.8, 4, 4.8, 8, 9.5, and then drops to 4 for f/22. Preview does much the same thing but less accurately, reporting a progression from 0.97 to 6.5, but then dropping to 6 for f/22.

With the same non-coded lens, but the lens data manually entered incorrectly as 90/2, LR gave the apertures as 2, 2, 2.8, 4.8, 5.6, 8, 9.5, and 4. Preview gave them as 2, 2, 2.97, 4.5, 4.96, 6, 6.49, 4.

I am completely baffled. Anyone have an answer? How do the programs derive a value for f/stop? Since LR and Preview report different apertures for the same exposure, it can’t be just information supplied by the camera. The camera knows what the maximum aperture of each lens is, but what, the camera or the program, or both, decides that a lens is set to that, or to anything smaller?

—howard


> On Feb 11, 2016, at 6:07 PM, Tina Manley <images at comporium.net> wrote:
> 
> Yes, my LR EXIF has aperture information for every photo I've taken when
> the lens information is supplied by the 6-bit code.  That's true for all of
> my digital M's.  It's usually in the ballpark but this time since I knew I
> had only used the lens wide open or at f/8, I noticed particularly that the
> apertures were wrong.
> 
> Tina
> 
> On Thu, Feb 11, 2016 at 6:03 PM, Howard Ritter <hlritter at bex.net> wrote:
> 
>> Tina—
>> 
>> An M has no way to sense what aperture the lens is set to. There’s no
>> mechanical or electronic link from the aperture to the camera. The camera
>> reads the 6-bit coding to know what model the lens is, and the cam gives
>> focus information to the camera, but that’s it.
>> 
>> I saw the aperture reported in the EXIF for your Beard’s Bread image on
>> Pbase, but unless that was manually entered, I can’t imagine where it comes
>> from.
>> 
>> Have you seen LR, PS, or any other program appear to be reporting aperture
>> in the EXIF of an image made with an M?
>> 
>> —howard
>> 
>> 
>>> On Feb 11, 2016, at 12:48 PM, Tina Manley <images at comporium.net> wrote:
>>> 
>>> PESO:
>>> 
>>> I did some tests with the Noctilux and Summilux on the MM and M246….I
>> did notice that neither camera
>>> records the aperture correctly because all of the photos were either shot
>>> wide open or at F/8 and they were not recorded that way.