Unsuitable lens profile in the M11

[don daniel]

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I am a newly happy owner of an Apo-Summicron 35mm. As you know, even this dream lens is not perfect and needs a lens profile that is automatically selected in the camera body. The profile is supposed to reduce or brighten the vignette (which is quite obvious especially at open aperture). I find that this happens on the M11, but unfortunately a blue cast is added. So the vignette turns out brighter, but gets a blue tint.

I checked this on my own M11, on an additional M11 and on an SL from my Leica dealer: the result is the same everywhere and you can already see it in the SL's electronic viewfinder: the vignette is blue.

I tried a normal Summicron 35mm asph. in the Leica store for comparison. This lens is also automatically recognized by the camera and the correction of the vignette takes place without color cast!

My hypothesis is: Leica screwed up the lens profile for the Apo SC 35.

I don't currently know anyone who has an Apo 35 and could verify this. I am writing this in the M11 section and not in the lens section because I don't think it is a problem with the lens. My Apo 35 performs superbly. I was also able to eliminate this blue tint with a trick: I made the lens code unrecognizable to the camera with a thin white adhesive strip and then selected the profile of the Summicron 35mm asph. in the M11. This profile causes a brightening of the vignette without blue coloration. Effect is however that in the EXIFS only no longer the Apo 35, but the SC 35 asph. is written as used lens. That is a pity. But it's bearable.

Maybe someone of you who has an Apo 35 could also do a test on a white wall: DNG, open aperture, white balance set in the middle of the frame. You can see the comparison from me between the original profile for the Apo 35 (first picture) and the manually selected profile for the SC 35 asph. (second picture) in the M11.

I want to emphasize that I see the blue coloration of the vignette depending on the background also in normal photos, not only in test shots on a white wall. I think it is unlikely that my lens is defective, because the coloration can obviously be corrected by a different profile. But it is awkward to select this other profile because I have to trick the camera to do it.

So I would be glad if someone with access to the Apo 35 could try this and maybe confirm it. Spontaneously, it seems abundantly absurd to me that Leica should not manage to generate a suitable profile for this flagship lens.

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Edited May 17, 2023 by don daniel

[adan]

What ISO are you using?

It is the case that Leica has always adjusted the amount and form of vignetting correction according to the ISO in use, starting with the M9 - because the noise in the corners will go 'way up as they are artifically brightened by the profile.

Effectively, a full correction for, say, two stops of vignetting on an ISO 6400 picture will result in the noise of an ISO 25600 exposure in the corners (brightened or "amplified" two extra stops 6400 > 12800 > 25600).

So the higher the ISO used, the less the correction profile is applied, by intention.

Are you shooting in full-spectrum (sun) light, or indoor lighting?

Correcting the WB to remove any yellow from indoor lighting can also amplify blue noise (the blue pixels are effectively far under-exposed and nearly black until white-balancing brings up the blue (often with a LOT of blue noise produced, as with the overall correction). Increasing color noise reduction in post-processing can get rid of blue in vignetted corners (or any shadow area) to some extent.

HOWEVER - it is also the case that even the "base" correction provided by the camera can sometimes be imperfect.

It took Leica about a year to "perfect" the vignetting and color-vignetting corrections for my 21mm Elmarit-M on the M9 a dozen years ago, in about the 4th or 5th firmware update. So you may want to email Leica with some samples to show the problem (including copies of the original .dngs), so that they can adjust the firmware eventually.

Edited May 17, 2023 by adan

[don daniel]

The shots above were taken outdoors with ISO 64, aperture wide open on a rather cloudy day.

[scott kirkpatrick]

DNG ?  What color temperature did the auto exposure assign?  Cloudy daylight is rather high in K temperature.  I have an APO 35 and have not been troubled by this, but I am happy to test.

Three tries on white walls indoors with daylight under clear skies coming through the windows,. produced color temperatures from 4000 to 4600 and neutral to slightly warm casts.  No blue but this is not cloudy shaded sunlight.

Edited May 18, 2023 by scott kirkpatrick

[don daniel]

I shoot DNG and set white balance in Lightroom. Auto white balance in camera does not seem reliable to me. Could you show a picture as a result, shot wide open?

[elmars]

vor 9 Stunden schrieb scott kirkpatrick:

Three tries on white walls indoors with daylight under clear skies coming through the windows,. produced color temperatures from 4000 to 4600 and neutral to slightly warm casts.  No blue but this is not cloudy shaded sunlight.

Hi Scott,

I have had a little discussion with Daniel about the problem. It's about blue shifts at the edges of the image, where the lens vignettes. It would be nice to have other camera/lens combinations than just Daniel's. Maybe you can narrow down the problem that way.

Elmar

[scott kirkpatrick]

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Every lens/camera pair requires its own profile.  Let's fix the lens to be the 35 APO Summicron.  To get the most vignetting, focus set at infinity, since the target doesn't have to be sharp.  I can use M11, M10-R and M10-D.  Only daylight source.  Today we have blue skies (4000-4500K), tomorrow rain is expected, which offers higher K light.  I'll include a WhiBal card as a reference neutral surface and bump exposure compensation +1.  Sound OK?  Talk to you in two days.

ISO 64, or both 64 and 400?

Edited May 19, 2023 by scott kirkpatrick

[elmars]

Adan says that the profile works different at different ISO. So 64 and 400 would be good. 

[ianforber]

I only have the CV 35mm f1.5, the vignetting of which I can reduce by selecting the 35mm Summilux profile in the M11 list of profiles. I’ve never noticed a blue shift in the corners but only ever view the shot after importing into Capture One - but probably have never taken a shot where it would be noticable. Obviously, an expensive Leica lens should be properly corrected when used with a Leica camera but do you notice the effect once imported into your processing software? 

[don daniel]

vor 3 Stunden schrieb ianforber:

Obviously, an expensive Leica lens should be properly corrected when used with a Leica camera but do you notice the effect once imported into your processing software? 

As I wrote in my post above, I see the effect even with normal photos. It is not my hobby to photograph white walls. But clearly, if you take a landscape shot, a green field below, blue sky above, then even if you choose to use open aperture, you will hardly see a blue cast in the vignette, simply because a blue cast in the blue or green is not really visible. But if you have a street scene or are shooting indoors, then you can see if the vignette is getting neutrally darker or if it has a color cast.

[elmars]

The 35 mm Apo is a nearly perfect lens, so it should have a nearly perfect profile. 

[don daniel]

Another comparison: both shots with M11 and Apo-Summicron 35mm. First shot with the original lens profile for the Apo 35mm. Second shot with the profile of the Summicron 35mm asph. I do prefer the "wrong" profile! Both shots have equal white balance: temperature: 6400, tint: +4. These shots are taken just to show the problem. This is not photography.😀

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Edited May 20, 2023 by don daniel