Leica Fotos app shows wrong f-stop from my M10-P

[Patrik]

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I have used the Fotos App with success from my Q but have just received my M10-P Reporter and just taken a few test shots at f/1.4 but in the App it shows being taken at f/4. All other info is correct.

How do I solve this?

Many Thanks in advance,

 

Patrik

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[FrozenInTime]

@PatrikThe aperture value is not electrically coupled between the lens and camera, so the camera estimates aperture based light hitting an optical sensor above the lens mount. The angle of view will likely differ between the lens and body sensor; the result may be closer if you test with a uniformly lit wall.

i.e. there is no complete solution !

 

Edited February 7, 2021 by FrozenInTime

[Patrik]

Ahh! Had no idea! Thank you! Now I know!

Just thought it could upload all info. 

👍🏻🙏🏻

[scott kirkpatrick]

Uploading over Fotos isn't the problem.  It's that estimating the aperture by comparing what two light meters see, one inside and one outside the camera, isn't always accurate.  The same errors will appear in the EXIF.

[adan]

12 hours ago, Patrik said:

Ahh! Had no idea!

Yep - the Leica M cameras use an absolute minimum of connections or "communications" between the lens and camera, to maintain compatability with legacy Leica lenses dating back to 1954 (or earlier, if one uses adapted screw-mount lenses from the 1930s-40s).

You can dismount your own lens and study it and the camera, to find the connections for yourself.

It is Leica's goal that (with a few exceptions) the oldest M lenses and the newest M lenses can be swapped between a 2021 M10-P and a 1954 film M3, while retaining near-identical functionality without modifications.

It is also Leica's goal that M lenses contain virtually nothing except structural metal and glass - no space wasted on wires, circuit boards, gold contacts or other electrical parts. Since there are thousands if not millions of legacy lenses that do not have those. And thousands if not millions of M film bodies that can't use them.

There are two mechanical connections for: 1) rangefinder focusing and 2) automatically displaying the correct viewfinder framelines, that date to the original 1954 cameras. Via the same levers and cams and rollers used ever since.

The only thing added to the lenses for digital use (or more accurately, for digital convenience, since it is not absolutely required) is the 6-bit "bar-code" of black and white dots on the back of the lens, which tells the camera, by way of a reader in the camera's lens flange, exactly which lens is mounted. Since the bar-code is literally paint, it does not change as the aperture is adjusted.

Meanwhile, on the camera, the little round external light sensor was added to compare the brightness coming through the lens with the actual metered scene brightness, to make an "educated guess" at the aperture used. If the lens is set to f/1.4, both will be nearly identical in brightness, whereas if the lens is stopped down to f/11, the internal meter will see a much darker version of the scene.

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[Patrik]

As I shoot with 6-bit coded lenses, I thought f-stop info was transferred as well. 

[AndreasG]

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vor 37 Minuten schrieb Patrik:

I thought f-stop info was transferred as well. 

Unfortunately not, such information is not transferred via the 6-bit code.

[scott kirkpatrick]

4 hours ago, Patrik said:

As I shoot with 6-bit coded lenses, I thought f-stop info was transferred as well. 

And ask yourself -- How can you transmit the current f-stop in six painted black and white dots?  It's asking a lot to have them just identify which lens you are using, since they only can express  64 combinations.

Edited February 8, 2021 by scott kirkpatrick

[jaapv]

3 minutes ago, scott kirkpatrick said:

And ask yourself -- How can you transmit the current f-stop in six painted black and white dots?  It's asking a lot to have them just identify which lens you are using, since they only can express  64 combinations.

Not quite, 3x64 because the frameline selector is involved as well, though you will have to subtract the WATE as it uses up three positions instead of one.

[scott kirkpatrick]

6 minutes ago, jaapv said:

Not quite, 3x64 because the frameline selector is involved as well, though you will have to subtract the WATE as it uses up three positions instead of one.

Well, the WATE and the MATE could be considered three lenses each.  I haven't used a MATE, but doesn't it shift the frame lines for you, using up three of the slots on your extended scale.  The WATE, on the other hand, doesn't change the frame lines, since 16-18-21 lies outside of all of them.  Anyway, to get all 3*64 possibilities into play, lenses with different focal lengths would have to use the same six bit code.  That hasn't happened yet, as far as I know.

Edited February 8, 2021 by scott kirkpatrick

[jaapv]

36 minutes ago, scott kirkpatrick said:

Well, the WATE and the MATE could be considered three lenses each.  I haven't used a MATE, but doesn't it shift the frame lines for you, using up three of the slots on your extended scale.  The WATE, on the other hand, doesn't change the frame lines, since 16-18-21 lies outside of all of them.  Anyway, to get all 3*64 possibilities into play, lenses with different focal lengths would have to use the same six bit code.  That hasn't happened yet, as far as I know.

The MATE shifts framelines automatically -or is supposed to, some series one examples were quite temperamental in this respect-; the WATE uses none, as there are no framelines to show. You need a Frankenfinder for that. Changing the EXIF value requires the menu. However the correction does not change across the three focal lengths (the MATE does).

Leica has indeed not used duplicate codes for different lenses (yet), as there has been no need, but the option is there.

[adan]

6 hours ago, Patrik said:

As I shoot with 6-bit coded lenses, I thought f-stop info was transferred as well. 

The code transfers only the maximum aperture built-in - it more or less decodes as something like "Leitz 28mm Elmarit-M III f/2.8" or "Leica 28mm Elmarit-M ASPH. f/2.8"

But paint cannot transmit whether you have set the lens to f/2.8, f/5.6, or f/11. The camera has to guess.