cl: no f-stop exif with coded lens and m adapter

[scott kirkpatrick]

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I haven't ever been able to keep a notebook with my exposure notes (or even with names of people photographed for use in captions). If I am uncertain what f-stop will give me enough depth of field for a picture, I usually shoot it at several stops. I can generally remember where I started, and the different shutter speeds that result tell me what the other settings were.

The M cameras and the SL have a "brightness sensor" pointing forward on the front surface of the camera.  On an M it is the little blue dot near the rangefinder opening.  On both the SL and SL2 there is a little window on the top left side behind which are an LED (AF assistance) and a sensor.  The two cameras have exactly the same parts for this function, so I assume that the same firmware is used for both.  The camera compares the amount of light reaching the front of the camera with the light reaching a similar sensor inside the camera, and uses a table to turn that those two values into an estimate of the f-stop that the lens is set to.  The CL does not have an external brightness sensor.

If you get your fingers in front of the external sensor, strange things can happen.  It is easy to do on the SLs, and a bit harder to do with an M.  When the M's were new, I would put my finger over the blue dot, making it think that it was nighttime out, and see what aperture it estimated.  There is a table in the firmware listing the maximum aperture for each lens, and this value should result.  It used to be not uncommon to find that a lens would report its aperture as 1.0,  or 0.0 when Leica had not checked these entries very carefully in the firmware, since they also don't think this is terribly important for taking good pictures.

So just now I took some pictures with an R 80/1.4 on an SL set to f/4.0 with the external brightness sensor open and obstructied.  Open, the EXIF said f/4.0 (correct!), and obscured it said f/1.4 (also correct!).  I don't know how someone got a value of 0.95, as reported above.

Edited April 30, 2020 by scott kirkpatrick

[jaapv]

On 4/30/2020 at 1:24 AM, eev776 said:

Well, I guess Leica going to work on improving this to be accurate in SL2.

And how could they? The variation is not because of the inaccuracy of the software, that is precise enough, It is caused by variations in the light as measured by the image sensor and by the brightness sensor, caused by the contrast distribution of the subject, different angles of view, etc. Leica has no control over such parameters.,

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[jaapv]

12 hours ago, ramarren said:

Dau: Perhaps I simplify too much. I nearly always remember my lens opening ... It's always two stops down from wide open, as a rule. I only go to wide open when I need more light to get a shorter shutter time, or stop down a lot to increase DoF, and I can tell both of those situations from the photos I make. When I make adjustments like that, it's rare that I need to remember it much later since I remember the principle of what I'm doing rather than the specific settings... 

G

+1.

Usually I can make a pretty accurate estimate of my aperture, not from my rather fuzzy memory, but from estimating the light on the subject, and the shutter speed+ISO  in EXIF , combined with the look of the image.