It’s true, the photo data is wrong!

[Cheeseman]

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Hello folks,

I’ve been enjoying reading lots of forum topics since buying my first Leica a month ago.  The M10p is a revelation after a few years in the Sony world getting confused in settings and menu choices rather than taking photos.

Unfortunately one of the few settings on the M10p I have looked at seems to be giving the wrong aperture reading on the Fotos app and subsequently this follows through in Lightroom.  For a time I thought I must be remembering how I took the shots incorrectly, but today I was in Sunny 16 and the photo data shows an aperture varying between 5 and 8.  I just did a test and uploaded a single photo to Fotos taken at 16 and it comes out as 5.

I’m almost certain that the camera doesn’t change the aperture without telling me (!), do I have a dodgy Summicron 50 or camera?  My other lens is a Summicron 75 and I haven’t checked that one yet.  I’m thinking if that’s also erratic then the issues lies with the camera.

Thoughts most appreciated,

Richard

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[jaapv]

Any Leica M does NOT know the exact aperture as it is mechanical with no linkage to the electronics. The camera guesstimates by comparing exposure with an external light meter, but that can be as much as two stops off. 

[Cheeseman]

Wow, that’s a characterful quirk I didn’t know about!  

It seems more than two stops of being 16 down to 5 to 8 ish, but so long as there’s no malfunction then I’m happy.

Thanks very much for the quick reply Jaap.  As I said before, I’m only a month in but I find the camera and the Rangefinder method of shooting both engrossing and compelling.

Cheers,

Richard

 

 

[adan]

If you look at the back (the mount) of any M lens, you will soon see the only "communication" between the lens and the camera is 1) the metal focus cam that moves in and out to focus, and 2) if included, simple black and white spots of paint to code the lens for recognition of type and maximum aperture (e.g. f/2.0)

There are no electrical contacts - or even mechanical means - to link the aperture being used to the camera. Been that way for 66 years, and Leica really did not want to tear apart all those lenses and start over for digital. They'd rather keep the solid brass, rather than drill a lot of holes for wiring. Thus a guesswork workaround - which will work (approximately) with ANY lens since 1954 (or with adapter, any lens from 1930 or so).

One big gotcha is that the external reference meter (the tiny round window on the top front, in line with the hot shoe) has a fixed field of view. It doesn't always "see" the same part of the scene as the TTL meter. So yes, a wider or longer lens, or the pattern of brights and darks in the scene (skies, walls, faces) will result in erroneous guesses, that can be large.

Especially if one accidentally covers the external sensor with one's finger.

Does not affect the actual exposure indicated, which is soley based on the internal meter..

[hteasley]

1 hour ago, Cheeseman said:

Thoughts most appreciated,

The aperture is a guess. There's no coupling between lens and camera that tells the camera what the aperture is. The guess is based on the shutter, the ISO, and the histogram of the image as shot.

Edited August 3, 2020 by hteasley

[Tailwagger]

You might also be interested to know that following the M240,  the M10's original firmware removed the aperture guestimate feature, no doubt due to some vocal complaining about its lack of accuracy.  Thankfully, IMO, after more complaining, it was reinstated. It's not perfect but a rough guess can be useful, particularly when reviewing shots taken from months or even years ago.

One of the subtle advantages of the aperture guessing for me has been that it forced me to become far more cognizant of my aperture selection to the point where my process and the way I think has been altered over time. I began limiting myself to full stops as it was far easier to remember from the field into post. It's rather rare that I'm so concerned with DoF that I worry about the effect of 1/3 or 1/2 stops. There are a few circumstances where I violate this self imposed policy, but generally, unless the scene forces a compromise between speed and DoF,  I keep to my full stop rule. By reducing the number of choices I allow myself,  I've built over time a more accurate mental model of what I will get from the use of a given lens at a given aperture when focused close, mid or at infinity. An unintended benefit, but sometimes, as they say, less winds up being more. 

Edited August 4, 2020 by Tailwagger