I am using Lightroom version 4.4 on a Mac OS X 10.7.5.
When performing a search for pictures based on the Aperture size as the criterion, the aperture sizes that are displayed by Lightroom version 4.4 are not correct for the Noctilux 50mm f/0.95 lens.
Does anyone have the same problem? Is there a solution to the issue?
I believe this is a manual lens and has no electrical contacts to tell the camera what the aperture is set to, so the camera cannot embed the aperture value in the photo EXIF.
Are you using software to put an aperture value that you've written down, somehow, into the EXIF afterwards and LR is not reading this correctly, or how would LR know the aperture the lens is set to?
Yes, you are right, it is a manual lens. However, the lens is 6 bit coded. Therefore, it is my understanding that the information on the type of the lens, shutter speed and aperture of the shot is recorded as the metadata (digitally on M9) which is then read and shown by the lightroom.
The “six-bit-code” is just a barcode of black or white paint streaks, that encode a lens-ID, so the camera can understand which lens is mounted and can store things like maximum aperture and focal length in the EXIF, but this is not a way to communicate parameters that vary per shot like aperture and subject distance. Unless there are actually electrical contacts then there isn’t any variable information that can be communicated.
It is possible for software to "guess" at the aperture by measuring the light on the sensor and using the exposure time and ISO to arrive at what the aperture might be. However, it's a guess, and it's not a direct measurement so it could be off.
I think Leica actually will embed this information in the maker notes section of the DNG file and Lightroom will use that data. It's using Leica's best guess, but it's impossible to get the actual data as it doesn't exist.
Does the camera measure light independent of the lens or does the lens only stop down to the selected aperture at the time the shutter is pressed and is wide-open otherwise? Or what known aperture or light-level does it compare against to guess the aperture?
To answer my own question, the M9 uses an exposure reading external to the lens to compare with the light coming through the lens to estimate the aperture-setting of the lens:
"The reported f/stops in the M9 EXIF are a guesstimate based on comparing the scene illumination as read by the little blue dot above the Leica logo with the ttl illumination as read by the internal meter..."
#3: "...there is no communication between the mechanical aperture & the electronics of the camera, so the data is derived & not all that accurate, particularly in low light..."