304 replies to this topic

[sharkmelley]

The first exposure should have the back-of-camera histogram right of centre.  Then successively halve it.

 

Bias frames are not required because the bias level is stored in the EXIF (600 for the Nikon D750)

[UKalwayscloudy]

OK. I can get the first histogram at that place
with a variety of exposure times by adjusting the panel power. If you don’t care about the actual times used to get there I’ll start around my usual 2s and halve from there. I’ve seen claims elsewhere that flat quality varies with exposure time even even if the histograms are placed right. Bias understood.

[savitar]

Thank you for your time and effort, Mike. I have read 90% of this topic, and the solution for the colored rings is so simple that I cannot believe no one (Nikon developers) seems to care enough to address it by simply turning off one feature for the RAW files with a simple firmware update. That is a big shame for Nikon.

 

I do not know if I feel sad or glad about finding this topic lol

 

I have been using a modified D5300 for two years (never seen any artifacts) and have built a decent Nikon ecosystem around it. I was looking to upgrade to full-frame and mirrorless, planning to buy the Z6 II, and I am really disappointed about the color ring problem.

 

Since I already bought a new 15-30mm full-frame Tamron lens and have the Nikon ecosystem, I will go for the Z6 II or Z7 II anyway. I am not as professional as you are, but knowing these issues may prevent me from wasting potential future data.

Edited by savitar, 03 December 2024 - 12:58 PM.

[sharkmelley]

My advice is that if you haven't hit these problems then don't worry about it. 

 

However, if you do hit the problems then follow my suggestions in the section "How to reduce the effect of the rings" here:

https://www.markshel...correction.html

Edited by sharkmelley, 03 December 2024 - 06:05 PM.

[savitar]

We had a clear night tonight, so for the sake of interest I took a series of dusk sky flats at ISO 100 at every shutter speed from severely underexposed (1/1250sec) to slightly overexposed (1/6sec). 

 

Here is a montage where I've divided the blue channel by the green channel and stretched the data by a factor of 25:

 

BlueDivGreen.jpg

[click on image for larger version]

 

For the same files here is the red channel divided by the green channel with the same data stretch of 25:

 

RedDivGreen.jpg

[click on image for larger version]

 

I don't think I've got much more to say on the subject and I've still got no idea of the cause of these artifacts.  I think I've disappeared down this particular rabbit hole for too long.  It's time to re-emerge

 

Mark

Edit: I found your blog post and sent the sample NEF file.

Hi Mike Can You send me the raw file that Rings in it, I am contacting with Nikon about this and they are asking for a raw Image

 

My EMail

batuhanozmen98@hotmail.com

Edited by savitar, 05 December 2024 - 04:00 PM.

[sharkmelley]

Edit: I found your blog post and sent the sample NEF file.

Hi Mike Can You send me the raw file that Rings in it, I am contacting with Nikon about this and they are asking for a raw Image

 

My EMail

batuhanozmen98@hotmail.com

Take a look here:

https://drive.google...b5FdbUtmcp8_vxV

 

I've uploaded 3 consecutive flat frames from the sequence in post #85 and the "real world" example from post #88

 

Mark

[doc6]

I own a modded Nikon Z6, and decided to take a large number of overexposed and underexposed flat frames at ISO 100 with a tracing panel. After bias subtraction, I stacked the flat frames into an underexposed and overexposed master, and divided one by the other to isolate the rings more easily.

The red and blue channels go as expected:

 

 

But the green channel...

 

 

It's an absolute mess. The frequency of the small rings, and the 'wedges' to the sides seem to change with exposure too. Here's another example

 

 

This is definitely another in-camera correction.

I really don't know what to make of this. I've made sure that any menu option that might alter the raw files was off, but this strange pattern persists. It seems to have the same behaviour as the rings in the other channels; as the exposure level increases, the rings occur at a higher frequency and become less noticeable. What's really strange is that the green channel isn't supposed to have these corrections. On Mark's site, the Nikon Z6 is listed as only having corrections in the red and blue channels, and I haven't seen anyone else demonstrate this pattern.

Please let me know if there's something I missed T_T

 

Mohammed.

[sharkmelley]

On Mark's site, the Nikon Z6 is listed as only having corrections in the red and blue channels, and I haven't seen anyone else demonstrate this pattern.

Please let me know if there's something I missed T_T

I'm always pleased to see others reproduce the problem because peer review is important.  I have only seen problems in the green channel when lossy compression is switched on.  Is it possible that's what happened here?  If not, I'd be very interested to see one of your underexposed raw files and overexposed raw files if you upload them to a filesharing site.  One of each should be sufficient.

[doc6]

I'm always pleased to see others reproduce the problem because peer review is important.  I have only seen problems in the green channel when lossy compression is switched on.  Is it possible that's what happened here?  If not, I'd be very interested to see one of your underexposed raw files and overexposed raw files if you upload them to a filesharing site.  One of each should be sufficient.

Hi Mark, thanks for your reply!

I've always made sure to use lossless compression, however even the uncompressed raws exhibit this pattern.

I'm happy to share some of my raw files, though for some reason I feel like my flats aren't as 'clean' when it comes to showing the rings. I've always had to stack a bunch of flats to make the rings apparent, so I'll share the stacks too just in case.

 

https://drive.google...Ni9?usp=sharing

[sharkmelley]

Thanks. With your data, I can reproduce exactly what you are seeing.  I'm off to enjoy New Year's Eve events now so I'll give it more thought/investigation tomorrow.  Happy New Year!

[sharkmelley]

According to the EXIF header, corrections are switched off but the firmware version of your Z6 is 3.40, which is a more recent version than previous results I have seen.  It's quite possible that this firmware version behaves more like the Z6II which does have a correction applied in all 3 colour channels ( https://www.cloudyni...4#entry12577695 ) instead of just the red and blue channels.

 

I have never previously seen the wedge/hyperbola artefacts and I don't know what they are. 

 

The only advice I can give to reduce the effect of the concentric banding in long exposure deep-sky imaging is my usual advice of using a high ISO (e.g. ISO 1600) and adjust exposures so the peak of the back-of-camera histogram is approximately central.  Flats should be shot with the histogram well over to the right.

[doc6]

According to the EXIF header, corrections are switched off but the firmware version of your Z6 is 3.40, which is a more recent version than previous results I have seen.  It's quite possible that this firmware version behaves more like the Z6II which does have a correction applied in all 3 colour channels ( https://www.cloudyni...4#entry12577695 ) instead of just the red and blue channels.

 

I have never previously seen the wedge/hyperbola artefacts and I don't know what they are. 

 

The only advice I can give to reduce the effect of the concentric banding in long exposure deep-sky imaging is my usual advice of using a high ISO (e.g. ISO 1600) and adjust exposures so the peak of the back-of-camera histogram is approximately central.  Flats should be shot with the histogram well over to the right.

I've managed to downgrade my Z6 to version 2.20, and I'm still getting the same pattern in the green channel :|

 

 

I guess they might have introduced this 'correction' in an earlier version, seeing as the camera was released in 2018. Actually, do you mind telling me the firmware version of your Z6? I might try downgrading to that and see what happens (if I can find that firmware on the internet T_T).

 

[sharkmelley]

Wow, that is annoying!  My version is 02.00

 

Do you have any other lens (adapted or not) that you can test with?

[FrankieT]

I might try downgrading to that and see what happens (if I can find that firmware on the internet T_T).

Here is useful resource for older Nikon firmware - Nikon Z6 v2.00.
 

[doc6]

Wow, that is annoying!  My version is 02.00

 

Do you have any other lens (adapted or not) that you can test with?

No :c I use a NIKKOR Z 35mm f/1.8 S, which the camera recognises, so that might be the issue. I'll try taking a series of 'flats' without the lens on, and see if a similar pattern arises.

 

Here is useful resource for older Nikon firmware - Nikon Z6 v2.00.
 

Thanks, but I've already downgraded to version 1.01, to no avail. Still the exact same pattern. I don't think this has anything to do with the firmware, unfortunately.

[sharkmelley]

I'll try taking a series of 'flats' without the lens on, and see if a similar pattern arises.

Another possibility is to tape over the electrical contacts.  But I don't know what aperture setting the lens will use in that case.

[doc6]

Another possibility is to tape over the electrical contacts.  But I don't know what aperture setting the lens will use in that case.

I'm afraid that's not an option. This lens uses focus by wire, which makes it impossible to fine tune its focus without electricity. Even if I set the focus beforehand then tape over the contacts, the aperture just closes up when the camera's turned off. soooo ¯\_(ツ)_/¯  guess I have to live with this now, which is a huge bummer considering I'm imaging 35mm wide field under Bortle 7-8. 

Ironically imaging untracked gave me much better results, as I could actually image with the histogram peak at a third from the left edge, with any ring pattern getting smeared into an easily correctible gradient.

Such is life T_T

[sharkmelley]

I'm afraid that's not an option. 

I didn't mean tape over the contacts for imaging runs but just for taking a set of flats without the lens being recognised by the camera, to see it it makes any difference to the pattern.

[doc6]

I didn't mean tape over the contacts for imaging runs but just for taking a set of flats without the lens being recognised by the camera, to see it it makes any difference to the pattern.

oh i am stupid

[doc6]

Alright, I can confirm that the pattern still appears in the green channel even when the camera doesn't recognise the lens. I'm completely lost at this point.

[sharkmelley]

Alright, I can confirm that the pattern still appears in the green channel even when the camera doesn't recognise the lens. I'm completely lost at this point.

It doesn't surprise me that the correction is applied even when the lens is not recognised.  However, I would be interested in seeing a raw flat file from that experiment.  

[SubaruB4]

I haven't seen all the posts here but I just got a Z6 so how does it do with capturing DSO?

[stars-Dust]

I haven't seen all the posts here but I just got a Z6 so how does it do with capturing DSO?

You can find the thread educational if you want

 

The only issue with some nikon cameras is the angular rings 

 

Some people say the issue does not show up with short exposures. Not sure if that is true. If it is true, then maybe cooling the camera might help.

 

 

https://www.cloudyni...300-m-settings/

Edited by stars-Dust, 26 June 2025 - 11:51 PM.

[sharkmelley]

I haven't seen all the posts here but I just got a Z6 so how does it do with capturing DSO?

If you already have the camera then it's worth giving it a try.  You may or may not find the Nikon coloured concentric rings to be a problem for your own style of imaging.

 

The only issue with some nikon cameras is the angular rings 

Angular rings?  It's certainly true that Sony cameras have coloured concentric polygons caused by a lens correction applied when the lens is recognised by the firmware.  But I'm not familiar with angular rings on Nikons.

[stars-Dust]

 

Angular rings?  It's certainly true that Sony cameras have coloured concentric polygons caused by a lens correction applied when the lens is recognised by the firmware.  But I'm not familiar with angular rings on Nikons.

I should have been more carful 

 

What I was referring to is the coloured concentric rings

 

I have read every post of yours about z6 because I also have a modded Z6. Also read the 113 pages of mmalik thread about the cooling and getting ready to implement TEC cooling in the back screen recess area.