[Leica] IMGS: Tests with MM and M246

[Peter Klein]

Howard: There is a little round sensor on the upper front area of the
digital Ms. The camera compares the amount of light this sensor receives
with the amount of light the main sensor receives though the lens, and
comes up with an estimated f-stop based on the difference.  Like any
metering system, it can be fooled if the area measured and averaged is not
actually average (e.g. a high contrast scene).

Leica has said that they don't consider the information accurate enough,
which I assume is why they don't put it in the standard EXIF field for the
f-number. Instead, it goes in the manufacturer's proprietary area. Some RAW
image editors see and transfer it to that standard field, and some don't.
There may be some difference in how the various editors interpret the
information, or how Leica derives it based on coding or manual entry.

What I don't understand is why Capture One displays my M8's estimated
f-numbers, but not my (MM) Monchrom.

--Peter

On Thu, Feb 11, 2016 at 5:35 PM, Howard Ritter <hlritter at bex.net> wrote:

> 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.
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information
>