19 replies to this topic

[Parcival19]

Had the first partially clear night in two weeks yesterday and also 3 moonless hours to burn so I packed my gear and went to my imaging spot.

It was my first time using guiding and polar aligning with a laptop, so that took a while but it eventually worked.

I originally planned to image the Sadr region but as soon as I had framed it up a lonely cloud appeared and made a beeline for....the Sadr region.

Really starting to miss having goto in my humble tracker (SWSA).

So I needed a new target. I'd already burned an hour of my 3 setting up and framing, so I decided on the blue horsehead which was just high enough at that point.

Framing that one went a bit faster and off I went. 

Not wanting to "waste" more time experimenting I stuck to 30s exposures although I need to expose my histogramms more to the middle because I'm starting to fight with the sensor artifacts of my Nikon Z6II. I bumped ISO a bit and started imaging.

Total guding error was around 2" which is fine for my imaging scale of 4,88 "/px.

 

Total integration time is 1 h 24 min.

My ring artifact showed up again. Also colored concentric rings.

There would be a lot more details but I had to crop almost half the image to get rid of the ring and then sacrifice some detail to get the colored rings out.

In the short term I need to play with exposure parameters, see how far I can push exposure time and ISO but I'll probably look for a new mount soon. There are some GEM28 and CEM26 for around 1000 bucks used availabe.

 

 

 

 

 

Edited by Parcival19, 20 April 2025 - 10:13 AM.

[Parcival19]

The original image stretched to see the ring. It's in all my images, using three different lenses. Sensor would be my guess. I have found someone else with the exact same artifact, which led me to blame the sensor:

 

https://www.cloudyni...-advice-needed/

 

 

 

 

[jonnybravo0311]

That's not a sensor issue. It's an optical one. 

[Zambiadarkskies]

Had the first partially clear night in two weeks yesterday and also 3 moonless hours to burn so I packed my gear and went to my imaging spot.

It was my first time using guiding and polar aligning with a laptop, so that took a while but it eventually worked.

I originally planned to image the Sadr region but as soon as I had framed it up a lonely cloud appeared and made a beeline for....the Sadr region.

Really starting to miss having goto in my humble tracker (SWSA).

So I needed a new target. I'd already burned an hour of my 3 setting up and framing, so I decided on the blue horsehead which was just high enough at that point.

Framing that one went a bit faster and off I went. 

Not wanting to "waste" more time experimenting I stuck to 30s exposures although I need to expose my histogramms more to the middle because I'm starting to fight with the sensor artifacts of my Nikon Z6II. I bumped ISO a bit and started imaging.

Total guding error was around 2" which is fine for my imaging scale of 4,88 "/px.

 

Total integration time is 1 h 24 min.

My ring artifact showed up again. Also colored concentric rings.

There would be a lot more details but I had to crop almost half the image to get rid of the ring and then sacrifice some detail to get the colored rings out.

In the short term I need to play with exposure parameters, see how far I can push exposure time and ISO but I'll probably look for a new mount soon. There are some GEM28 and CEM26 for around 1000 bucks used availabe.

 

What lens/scope are you using?  

[Parcival19]

That's not a sensor issue. It's an optical one. 

There was no light source when I imaged, but I've just now taken exposures with the lens cap on with the same parameters I've had for the lights. Put the camera next to a bright daylight lamp and took one shot from each side.

Here's the photos stretched in Pixinsight. Is that unevenness a light leak I'm seeing? Master Dark/Bias/Flat don't have a ring as far as I can see, at least not after a quick stretch.

The camera LCD is off during imaging and it's mirrorless so should not have a direct connection to the sensor from the viewfinder. (Nikon Z6II)

If yes, would the next step be to tape off every connection on the imaging train one by one and see what makes it go away?

 

 

What lens/scope are you using?  

It's a Redcat51 WIFD

Edited by Parcival19, 20 April 2025 - 12:23 PM.

[Zambiadarkskies]

I don't think it is optical but I am not sure.  I think it is in camera vignette (or lens) corrections in the image.  I have seen similar with my Canon R6.  

 

- are you taking flats? 

 

I cannot remember the exact circumstances that I have seen such patterns, but I have certainly seen them.  Are you certain that any corrections are turned off in camera?  I haven't followed your previous posts on the issue so apologies for any repetition.  

[jonnybravo0311]

Definitely looks like a light leak. There shouldn't be any visible brightness change - it should be uniform.

[Kerry D. Green]

The original image stretched to see the ring. It's in all my images, using three different lenses. Sensor would be my guess. I have found someone else with the exact same artifact, which led me to blame the sensor:

 

https://www.cloudyni...-advice-needed/

 

 

Screenshot 2025-04-20 1709143.jpg

Yeah, most likely the sensor.  See here:  https://www.markshel....html#NikonZ6II

 

There are things you can do to mitigate it.

[jonnybravo0311]

If anything, that points to software and data interpretation within the Z6 - not the sensor itself. The "split in the middle" is definitely the sensor's construction, but that's not what the OP is observing. It's a ring artifact, which certainly appears to be optical in nature, but I guess it's due to some image pre-processing done by the Z6. Mark's a much smarter guy than I am, and has certainly invested far more time and energy into analysis of cameras/optics than I have

[AstroFromHome]

Looks like a light leak to me.

The dark frames are definately contaminated by light. The ring that you see in light is 98% a reflection.

Try ant put a scuff tight over the full image train and take some new darks. If they get uniform you have a tiny leak. You may also check with Sharpcap. Do live camera and try tomfind with some flashlights where the image train is not fully sealed.

 

I had something similar with my 585M doing strange things. At the end it seems that it was a tiny light leak caused by a not visible unevenly contact surfaces between filter wheel and OAG. I put electical tape under the touching surfaces now and tucked the two pieces really tight together. Now the darks are even.

 

Real test under the stars is due to clouds still outstanding. The straylight at my place also ruined countless of hours of light frames that I had taken already while having that light leak. It has been round about 35-40h of integration time to be moved to the bin.

[Parcival19]

Looks like a light leak to me.

The dark frames are definately contaminated by light. The ring that you see in light is 98% a reflection.

Try ant put a scuff tight over the full image train and take some new darks. If they get uniform you have a tiny leak. You may also check with Sharpcap. Do live camera and try tomfind with some flashlights where the image train is not fully sealed.

 

I had something similar with my 585M doing strange things. At the end it seems that it was a tiny light leak caused by a not visible unevenly contact surfaces between filter wheel and OAG. I put electical tape under the touching surfaces now and tucked the two pieces really tight together. Now the darks are even.

 

Real test under the stars is due to clouds still outstanding. The straylight at my place also ruined countless of hours of light frames that I had taken already while having that light leak. It has been round about 35-40h of integration time to be moved to the bin.

 

I'm gonna see if I can find a source.

My darks from last night look uniform but those have been taken in dark environment. 

 

 

If anything, that points to software and data interpretation within the Z6 - not the sensor itself. The "split in the middle" is definitely the sensor's construction, but that's not what the OP is observing. It's a ring artifact, which certainly appears to be optical in nature, but I guess it's due to some image pre-processing done by the Z6. Mark's a much smarter guy than I am, and has certainly invested far more time and energy into analysis of cameras/optics than I have

 

Well, the one good thing about this is my gf said looks like I'll need a dedicated astro cam...

 

 

Yeah, most likely the sensor.  See here:  https://www.markshel....html#NikonZ6II

 

There are things you can do to mitigate it.

 

What would speak for the sensor/hardcoded processing is that I've already encountered the split sensor artifact in my last imaging session. It is conveniently in the middle of the ring. Also what's the chance that someone else has the exact same artifacts when it is in fact a light leak? Shouldn't it be a bit different? Although I have now found vignette control and diffraction compensation to be on. Maybe it was one of those?

 

Here's a lighntess layer from another image taken with this setup which shows the same ring with a split sensor artifact in the middle.

 

 

This user seems to have encountered the exact same thing: 

https://www.cloudyni...-advice-needed/

 

I don't think it is optical but I am not sure.  I think it is in camera vignette (or lens) corrections in the image.  I have seen similar with my Canon R6.  

 

- are you taking flats? 

 

I cannot remember the exact circumstances that I have seen such patterns, but I have certainly seen them.  Are you certain that any corrections are turned off in camera?  I haven't followed your previous posts on the issue so apologies for any repetition.  

Yeah, I'm taking flats, darks and bias frames. Although im only using the darks for cosmetic correction.

I thought I had everything turned off but I went throught the sub-menus again.

Vignette control was on, as was diffraction compensation unfortunately.

I'll see if that makes any difference next time I go out.

[jonnybravo0311]

Well, the one good thing about this is my gf said looks like I'll need a dedicated astro cam...

She's a keeper

[Zambiadarkskies]

I am betting on vignetting compensation!

[Parcival19]

I am betting on vignetting compensation!

That would make me pretty happy.
The forecast says partially cloudy tonight, would be perfect for running some tests.
I'll report back

[Parcival19]

Well, the plot on the light leak angle thickens.
Masked off all visible connections and did some more test photos next to my daylight lamp.
Still some light leak. Covered the whole imaging train up with a thick sweater. Light leak gone. So I steadily uncovered parts of the imaging train and did test photos until I got the culprit. It's the focuser or, to be precise, the little indicator window. Taped a bit of cardboard to it for now. No more light leak so far. Checked the other side of the Redcat as well but all clear as far as I can see in the stretched darks.




Left one is with the focus indicator covered, right one unconvered.



We'll see if that was the culprit after some real world imaging.

Edit: Partially cloudy apparently meant completely cloudy. So no testing tonight.

Edited by Parcival19, 21 April 2025 - 04:47 PM.

[Parcival19]

Had some semi-clear skies last night so I did some test-imaging.

 

Long story short...

 

Still there.

 

I pushed Iso to 3200 and exposure to 60s which got me a histogramm in the middle as advised for the Nikon artifacts. Vignette control and diffraction compensation off.

It's definitely a lot fainter than before and with enough target-signal I can sort of work around it a bit but annoying nevertheless.

No more split sensor artifact though.

 

I got a somewhat okay picture out of it. It's just 35 minutes with a stock mirrorless, for that I got a good bit of signal.

Not much smarter than before though. If it were a reflection, would it have been amplified with the higher ISO/gain? The longer exposure definitely tipped the SNR more in my favor. Could probably go a bit longer, guiding was below 2 arc seconds the whole time.

 

Uncropped image:

 

 

 

After the initial stretch, not obvious in the image but it's hiding in the luminosity layer:

 

 

[Parcival19]

Cropped to just the main attraction:

 

Edited by Parcival19, 23 April 2025 - 08:36 AM.

[T.M.E.]

I also have a Redcat51 WIFD and Nikon Z6ii and I ended up getting a 2600MC Pro cooled camera for the reasons you show here - I have seen similar circular artifacts. That said the Z6ii has a great sensor and seems to excel at widefield broadband targets so it has it uses - I just have to figure out what they are

 

FWIW I shot this with a Z6ii and 85mm 1.8 lens before I had the Redcat or 2600mc.

[Parcival19]

I also have a Redcat51 WIFD and Nikon Z6ii and I ended up getting a 2600MC Pro cooled camera for the reasons you show here - I have seen similar circular artifacts. That said the Z6ii has a great sensor and seems to excel at widefield broadband targets so it has it uses - I just have to figure out what they are

FWIW I shot this with a Z6ii and 85mm 1.8 lens before I had the Redcat or 2600mc.

That is actually good to hear, as strange as it sounds. If we have three people with the same camera and similar artifacts the sensor/software is looking like the most likely culprit so at least there's somewhat of an answer to the problem...

[T.M.E.]

That is actually good to hear, as strange as it sounds. If we have three people with the same camera and similar artifacts the sensor/software is looking like the most likely culprit so at least there's somewhat of an answer to the problem...

And its not always reproducible but seems related to Nikon's hardcoded image correction - Mark Shelly has some examples here. And like the one you linked, he has a lot of threads on CN looking at these issues - so what little I know is just from reading his research  

 

Along with the occasional split sensor artifacts it did make processing more challenging for me with the Z6ii and Redcat 51. It's also an under-sampled combination (4.88" / pixel) which may not matter much overall but all things combined I found processing data taken with the 2600mc a lot easier - at least for a beginner like me.

 

Would be great if Nikon made that particular image correction an option you could turn on/off. But I love the camera for daytime photography which i what i bought it for anyway. I do plan to try it some more this year on widefield/landscape targets and learn some more.