Weird webbing at high ISO in Q2M shots recovered 2 stops

[trickness]

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Just had my Q2M out tonight and shot at 25000 ISO, noticed that when I recovered two stops in Lightroom (as I exposed for highlights) I got a very weird webbing that almost looks likes sensor flare.  Anybody else experience this? I have read so much about the Q2m being able to recover several shots and provide clean images at high ISO that this has me puzzled. It is consistent across multiple shots under these conditions.

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[adan]

I see what you're seeing.

Looks like a moiré effect - although those are almost always with sharp textured subject detail creating an interference pattern with the digital pixel grid. Whereas this is mostly in the blurry areas.

https://en.wikipedia.org/wiki/Moiré_pattern

It could be some kind of reflection - those bright background lights reflecting off the pixels' microlenses to the sensor cover glass, and then back to the pixels, which would produce an "image" of the microlens grid that might itself moiré with the actual pixel grid.

Always remember that the Q-series adds pincushion distortion (curves lines) to images to eliminated the Q lens's own natural barrel (fisheye) distortion. Which could contribute to the "fanning out" effect.

I don't think pushing the image is causing this; it is just revealing it.

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[trickness]

4 minutes ago, adan said:

I see what you're seeing.

Looks like a moiré effect - although those are almost always with sharp textured subject detail creating an interference pattern with the digital pixel grid. Whereas this is mostly in the blurry areas.

https://en.wikipedia.org/wiki/Moiré_pattern

It could be some kind of reflection - those bright background lights reflecting off the pixels' microlenses to the sensor cover glass, and then back to the pixels, which would produce an "image" of the microlens grid that might itself moiré with the actual pixel grid.

Always remember that the Q-series adds pincushion distortion (curves lines) to images to eliminated the Q lens's own natural barrel (fisheye) distortion. Which could contribute to the "fanning out" effect.

I don't think pushing the image is causing this; it is just revealing it.

That is my suspicion as well. I’m just surprised as this kind of “sensor mesh flare” usually has been mentioned in use with direct sunlight, not low light/high ISO use. I really didn’t think pushing it two stops was going to be that big a deal, especially given that I only shoot in DNG. Those bright lights were very far away, it was pretty dark right where I took the shot.

Edited March 26, 2021 by trickness

[adan]

I think it is the contrasty lighting - really bright lights (relatively speaking) in the background are enough to produce reflections that show up against the inky shadows. Especially if you try to rescue them.

When you aren't pushing the image (more even, and overall brighter, lighting) the pattern stays relatively invisible.

[p-arrow]

Moiré is an artifact of the sensors grid playing with a dense pattern / very fine details. I don’t see a pattern in this image that would cause this. I’m pretty sure you’re seeing the limits of the sensor. 25000 iso + two stops is pretty extreme, even for a low light beast like the Q2M. I’ve noticed this exact pattern on Q2 colour images shot at high iso (though lower than 25000) and pushed similarly in LR. Most sensors I’ve pushed like this start to show banding noise in similar circumstances, and with the Q2s lens correction it gets that warped look to it. 

Obviously can’t be certain, but thats my best guess. 

[hdmesa]

Even on the Q2M, you can't underexpose by 2 stops then recover 2 stops at ISO that high without artifacts. That's all this is. When shooting the Q2M at ISO that high, make sure you nail the exposure.

Edited March 29, 2021 by hdmesa

[Leica Guy]

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When I have any doubt about exposure or the scene is obviously high dynamic range, I bracket exposure just to be safe. Then pick the one in post that I like best or protects highlights. 

[trickness]

Thanks all! Just finding the limits I guess!