Archived posting to the Leica Users Group, 2016/02/11

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Subject: [Leica] IMGS: Tests with MM and M246 - Howard
From: boulanger.croissant at gmail.com (Peter Klein)
Date: Thu, 11 Feb 2016 20:18:04 -0800
References: <CA+yJO1A2N2yntQ0J1OG8OQeg4qf1Dy3M-WqLpWnX4r__p_KL1Q@mail.gmail.com> <A6F75171-2092-4194-B0EF-F5DAD41908F4@bex.net> <CA+yJO1Dv6a2qvQfb5PLze8_jXcEZ9sHPYoLi5H9gmiFP2oN5hg@mail.gmail.com> <3AB42220-3DAD-4EFE-9778-EC5C43917265@bex.net> <56BD56DD.8050900@jayburleson.com>

Jay:  I mentioned this in the other thread that in which Howard's question
appeared, but I'll ask you here as well:

Do you know why Capture One displays my M8's estimated f-numbers, but not
my (MM) Monchrom's?

--Peter

On Thu, Feb 11, 2016 at 7:51 PM, Jay Burleson <leica at jayburleson.com> 
wrote:

> Top center left on the front of an M body is a small window which contains
> a metering cell that meters the environmental light, in order for the
> camera to be able to guesstimate the lens aperture. This is relevant for
> in-camera vignetting correction as well as EXIF data.
> It compares the light coming to it with the value of the max aperture as
> reported by the 6-bit coding and comes up with a (sometimes spurious)
> number. For example, use of the exposure compensation will really throw it
> off. I run -2/3 almost all the time on my MM and it reports to me that my
> Summilux wide open is f/1...
>
> Jay
>
> On 2/11/2016 5:35 PM, Howard Ritter 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
>>
>
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Replies: Reply from leica at jayburleson.com (Jay Burleson) ([Leica] IMGS: Tests with MM and M246 - Howard and Peter)
In reply to: Message from images at comporium.net (Tina Manley) ([Leica] IMGS: Tests with MM and M246)
Message from hlritter at bex.net (Howard Ritter) ([Leica] IMGS: Tests with MM and M246)
Message from images at comporium.net (Tina Manley) ([Leica] IMGS: Tests with MM and M246)
Message from hlritter at bex.net (Howard Ritter) ([Leica] IMGS: Tests with MM and M246)
Message from leica at jayburleson.com (Jay Burleson) ([Leica] IMGS: Tests with MM and M246 - Howard)