possible problem with aperture reading

[aneal]

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Hi

I am new to this forum .I have a M9 with the latest version of a f2 50mm summicron( non coded).Every time I open RAW files in lightroom the reading on the histogram states that the aperture reading is 2.4 or even 2.8 despite the lens ring reading f2.

Should I be worried or is that something that occurs a lot to other users?

The lens appears to work fine and there are no structural abnormalities with it.

thanks

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[ho_co]

Welcome to the forum, aneal!

 

It's a common question. Nothing wrong with camera, lens or software.

 

Since there's no diaphragm linkage between the body and lens, the camera is literally guessing. It compares the amount of light it sees through the blue dot at the front corner of the top plate with the amount of light its metering system is seeing, and checks the lens ID to find what the max aperture is. And then it guesses. It's amazing how close to accurate it usually is.

 

When you use an uncoded lens, you can get wild assumptions. But then, in 20 years you won't remember which lens it was, so they won't seem so wild any more!

[hydeca]

It's amazing how close to accurate it usually is.

 

Have you systematically tested how accurate the estimates are?

 

From my experience the accuracy varies from perfect (daylight with fast shutter speeds) to a long way off (low light with long shutter speeds) whether the lens is coded or not.

[jlindstrom]

I don't think anyone has really done that (besides Leica). For the most part, why do you care?

 

No pun intended in that one, but if the picture looks good and is what you envisioned/hoped to get.. why care? It's just a number after the fact. Of course sometimes it's nice to find images from your catalog with certain lens&aperture combo, but then "the guess" is pretty much good enough.

 

Technically it's a historical thing since there are no electronics in the lenses. For us users that's a good thing as it saves weight and size & adds reliability. All electronics fail at some point..

 

//Juha

[mby]

There's been extensive research on this very subject by Carl Bretteville from this forum; it's available here...

 

Best,

Michael

[delander †]

Carl's work was done using the M8. I did some brief tests and found that in general with the M9 the f number reported in the exif is a slightly smaller aperture than that actually used (down to f8). However the results vary not only on the lighting conditions but with the lens used. Small apertures such as f11 and smaller tend to get reported as f8.

 

Wide angle lenses get reported more accurately, but that is to be expected, is it not?

 

Jeff

[ho_co]

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Jeff--

Any idea why the M9's guessed aperture should differ from the M8's? I know you've mentioned the difference several times, as I think others have as well.

[delander †]

The M9 meters from one central white shutter blade and top and bottom grey blades, whereas if I remember the M8 has the central white blade but the others are black. Could this be the reason?

 

Jeff

 

Maybe. The measuring cell (limited angle of view) turns the M8 metering pattern into an ellipse with blurred edges in the horizontal, the grey blades were added to make it more of a blurred-edge circle. I don't think there is much difference in metering in real life, however.

[tander21]

I am using an M9 wth a wide angle lens, 24mm. I just noticed a problem with metadata in Bridge and Lightroom. I use aperture priority today set at f11. When I look at the metadata for the various shots some are f11 while others are f27! and f9! There are no problems with the images, but I set the f stop manually and assumed it would be reported consistently that way in the metadata.

 

Any suggestions on why such a large range?

[ho_co]

Welcome to the forum, tander!

 

No, don't expect consistency from the estimated aperture.

 

Remember, with film with these same lenses, we didn't even have a guess.

 

That does seem like a wide range. Once I realized it was only a guess, I quit worrying about the variations in inaccuracy, so that may not be unusual.

 

There are some programs that will let you go in and modify the metadata if it's important, though I don't recall what they are.

[Ario Arioldi]

There are some programs that will let you go in and modify the metadata if it's important, though I don't recall what they are.

Exiftool is one of those.

[mjh]

The M9 meters from one central white shutter blade and top and bottom grey blades, whereas if I remember the M8 has the central white blade but the others are black. Could this be the reason?

This change serves to compensate for the bigger sensor. The reflective zone would have to be 33 percent higher to compensate exactly, so three white shutter blades would have been too much. One white and two grey shutter blades are an approximation.

 

In other words: this change was necessary to bring the metering characteristics of the M9 in line with that of the M8 (if only approximately).

[aneal]

Thanks everyone for your advice so far.There is nothing wrong with the lens.The aperture readings on lightroom are clearly not accurate but after reading the posts I am not unduly concerned.