Lets Play Raw.
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_DSC5869.ARW.xmp (1.3 KB)
_DSC5869.ARW (23.5 MB)
_DSC5869.ARW.xmp (1.3 KB)
_DSC5869.ARW (23.5 MB)
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Could you please share the raw file.
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Sorry, I was so excited to post my 1st PlayRaw that forgot to include the raw file. 
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Here is my DT 5.4 AgX version. Am I mistaken or is this image underexposed in the camera? It loaded very dark in DT and required over 4EV exposure adjustment. Would the noise be decreased with a brighter exposure on your Sony camera or is it ISO invariant? Just wondering.
_DSC5869.ARW.xmp (12.2 KB)
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Yes. It was underexposed. could not miss the shot. I did not wanted to go to higher iso and did not have my tripod with me. Camera is old Sony a6000 and is very noisy at higher iso. The colors were too beautiful to miss it.
BTW, I know I will be grilled for it but I did another version of it with two instances of AgX and I liked the result.
Nice shot. I noticed it was slightly underexposed and there was a fair bit of noise so I ran it through the new RawRefinery denoiser and then did what I could with Darktable.
_DSC5869_denoised.dng.xmp (15.6 KB)
I attached the xmp file but it is probably useless because the denoiser put out a dng file.
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@kap55 One of the advantages of old eyes are that they don’t see noise. 
You would be surprised - I suspect mine are older than yours. In fact I just got a couple of new lenses (not for my camera) - one for each eye.
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I didn’t do much. darktable 5.4 and AgX
PS - Sorry, I looked at the raw file and assumed the photo was made when it was almost dark. After reading the rest of the thread, it seems it was just deliberately underexposed.
_DSC5869.ARW.xmp (8.0 KB)
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Well done. Almost same as the version I did with 2 instances of AgX.
With respect I suggest this is a common mistake that people make. This shot was taken at 100 ISO and you avoided higher ISO presumably fearing noise from higher ISO, but experience has taught me that with my Canon’s under exposure is a bigger source of noise than high ISO. I get less noise by raising the ISO to obtain a brighter picture. This is true for my Canon’s. I can not say for certain that it is true for your Sony. I would recommend testing this with your specific camera. My Canon is the worst of my cameras for underexposure ISO noise and my Nikons less so.
Fuji is my favourite camera that I don’t on because I love the flexibility of ISO invariance that seems to allow very underexposed images to be brightened in editing with no apparent increase in noise.
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You are right.
However, this way I had more flexibility. There are times that I wish to keep the image dark and underexposed and lower iso in those situations will have less noise. It is only when raising the exposure in post edit makes it nosier than if i would have raised initially the iso. In this case I was not sure what I would have get. The scene was too beautiful and color was changing very fast and I did not wanted to miss it.
As much as I love my old A6000 it is a very noisy at high iso.
I actually have experimented with what you suggesting and compared test images of low iso underexposed vs higher iso at proper exposure. Difference IMO is negligible vs the flexibility in a very fast loosing light.
BTW, You are turning on a fever that I am trying to put off and that is a justification for getting a camera that i have eye on.
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At least you have done the test. I often use manual exposure with auto ISO and bracketing. Then I can pick the best image to edit. This is my usually shooting from the hip exposure setting for when I travel.
I also find that with most digital cameras the quality difference between 100 and 400 ISO is non-existent but gives more flexibility with aperture, shutter speed and low light. I wonder if this is true for your camera.
I do also manual. I am more of control freak and want to control everything. Kidding a side, tried auto iso and was not satisfied with result. I had keep the upper limit not to more than maybe 400. I think this is weakness of older Sony cameras. There is a Leica that is smiling at me and I am trying to ignore it. 
Some cameras these days are nearly iso-invariant. So here is my simple-minded way of thinking about s/n in dark scenes.
I think of sensor noise as a floor. It’s not exactly true, but stay with me here.
Sensor signal depends only on exposure. Wide aperture and slow shutter give more exposure. Of course you know this…
Weak signal is increased by upping ISO. But the amplifier circuit also increases sensor noise in proportion. Amplifier circuits add noise but it tends to be modest.
So in this limit, the same exposure gives the same signal to noise, regardless of ISO. Just increase the post-collection exposure in your raw developer (dt etc), if needed.
There are some examples online. ISO invariance is only true up to a point. But it gives a starting point for thinking about exposure in dark scenes.
I’ve gone down this rabbit-hole because I shoot with an MFT camera. One can get nice exposures with low noise in dark scenes, at the expense of wide aperture and slow shutter speed. Fortunately, MFT tends to use shorter focal length, and IBIS can be excellent.
This is Play raw and I’m going off topic, but exposure on digital cameras is mostly governed by aperture and shutter speed, not ISO.
19mm 2.8 lens (28mm FF) 1/125 @ 4.5 ISO 100. Ideally you should have lower the speed to around 1/60 for hand held and maybe f4. It would still be underexposed, but with more signal in the sensor. For the future.