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Why aperture changes automatically on my 35mm Cron


Adalsteinn S.H.

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I have a question for you all that I hope that you can help me with.

 

I just bought a used 35mm Summicron ASPH (no coded) for my MP240 and have set Lens Detection to Manual and 35 f/2 ASPH (my lens is a 1182). When I finally had an opportunity to go out shooting this morning I used just to apertures, f/2,0 and f/4,0. But when I had a look at the images I shot I noticed that the apertures seemed all over the place showing f/3,4 , f/2,8 and even f/16 (took for example numerous shots at one spot and all of them show ISO200 - f/16 - 1/500 sec in LR).

 

Any idea what is going on here?  

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It has to do with the camera guessing at the apertures with relationship to metering.

The camera "guesses" at the aperture based on the brightness of the image.

 

There is no electronic connection between the lens and camera and the camera gas no idea what aperture is set.

The registration in the menu where you pic the lens records the lens mounted in exif and on some lenses allows for minor corrections.

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It has to do with the camera guessing at the apertures with relationship to metering.

The camera "guesses" at the aperture based on the brightness of the image.

 

There is no electronic connection between the lens and camera and the camera gas no idea what aperture is set.

The registration in the menu where you pic the lens records the lens mounted in exif and on some lenses allows for minor corrections.

 

 

Thanks for your swift reply. So the only way to counter this is to have the lens coded?

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M 240 (and co) has a sensor near the front logo to measure the light and compare this to the amount of light reaching the inside light sensor.

Coding or not a lens, no difference in the f stop calculated.

 

In M10, Leica don't offer that "F Stop in EXIF" anymore.

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Thanks for your swift reply. So the only way to counter this is to have the lens coded?

Lens coding will still not record aperture set on the lens. There is no way for the lens to tell the camera what the aperture set is.

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I have a question for you all that I hope that you can help me with.

 

I just bought a used 35mm Summicron ASPH (no coded) for my MP240 and have set Lens Detection to Manual and 35 f/2 ASPH (my lens is a 1182). When I finally had an opportunity to go out shooting this morning I used just to apertures, f/2,0 and f/4,0. But when I had a look at the images I shot I noticed that the apertures seemed all over the place showing f/3,4 , f/2,8 and even f/16 (took for example numerous shots at one spot and all of them show ISO200 - f/16 - 1/500 sec in LR).

 

Any idea what is going on here?

Just to be clear, actual aperture used (which affects DOF and exposure) is what you set on the lens..... only the recorded aperture is changing since it is a guess (M10 doesn't even try to guess, leaving it blank in EXIF).

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Just to be clear, actual aperture used (which affects DOF and exposure) is what you set on the lens..... only the recorded aperture is changing since it is a guess (M10 doesn't even try to guess, leaving it blank in EXIF).

Most of M10 users claim for bringing back this feature with one of the next firmware updates!

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Coding the lens will have no effect. The camera simply does not know the current aperture value of the lens.

It is not totally true. The coding will inform the camera of the maximum and minimum apertures available on the lens in use. Which means, as an example, that a coded Summicron will never show f1,4 as the aperture used, which can happen with a non coded lens.

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It is not totally true. The coding will inform the camera of the maximum and minimum apertures available on the lens in use. Which means, as an example, that a coded Summicron will never show f1,4 as the aperture used, which can happen with a non coded lens.

You have too much confidence in Leica FW coders. :D

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