Flats issue?

[stbkaiser]

Hi Robin
Running
Win 11 pro
SharpCapInstall-4.1.10885.0-64bit
Using ZWO ASI2400MC pro cooled color camera
Capturing lights using dither every 3 images.
I am using the Flats tool in sharpcap .
Setting the Bit depth and Gain to the same settings as my Lights
Following the settings instructions for the histogram per your help file .
Run with option to use Bias correction.
Capturing 40 images.
I have used a Light Panel and the white Tee-shirt method to create a master flat.
Stacking A set of Lights with DSS, 3 different ways.
No flats, with Tee shirt flats and with Light Panel Flats.

I then processed all three results in Photoshop, with the same steps. Final step is a adaptive stretch to exaggerate the differences. Not something I would do in normal processing. But I did this to help show the flats result.
From what I see , the T-shirt and Light panel flats give close to the same result , so I don't think the light panel is the issue.
Comparing the No flats image to the flats corrected images, it seems the flats do correct part of the image but introduce a different set of light bands.
Maybe I am expecting too much correction from using the Flats?

Any other suggestions, Ideas?
Thanks for help with this.

[admin]

Hi,

does the sort of '3d ripples' effect show up in the flat frames too? It's a very odd pattern and not something I'd usually expect to see as the result of vignetting, so I am just wondering what is causing it and if it is something that can be fixed by flat frames.

cheers,

Robin

[oopfan]

Hi Steve,

The Flats are working. It removed some dust donuts on the sensor. However, the large concentric circles look to me to be either (a) condensation on the sensor, (b) a light leak. I'm leaning towards condensation. Try imaging without the cooler turned on.

Brian

[stbkaiser]

HI
The cooler is running during the imaging session.
I believe -5 C
I converted a master flat to JPG and attached it .
I think it looks normal , concentric rings of differing gray scale as you go into the center.
The rings are more defined in Photoshop raw image but are softened when I converted to JPG to upload here.
I'm not experienced in using flats so maybe I am expecting too much.
Note that the Stacked image consists of about 3 hrs of exposure with a AT92 F/5.5 TRIPLET APO REFRACTOR .
I ran the same plan again last night to double the lights and the processed image did improve with less defined rings.
Weather permitting , I will run again and see how much it improves.
I will report back on progress.
Thanks

[admin]

Hi,

just looking at that flat frame, it seems much darker than I would have expected. The center area is only at about 25% of maximum brightness, which seems odd as normally I would expect a flat frame to aim for 70 to 80% brightness levels in the brightest areas.

It's also worth noting that the corners are about 10 times darker than the center, so you are unlikely to get perfect correction across the whole frame - your setup is obviously badly vignetted when using the large sensor of the 2400.

Finally, one more thing occurs to me. Is it possible that somewhere along the way you had the 'flip' setting different between the light and the flat frames? If the flat was misaligned due to different flip settings (or anything else that moved the sensor relative to the center of the light path) then you might expect weird effects like those seen in the images in the first post.

cheers,

Robin

[stbkaiser]

HI
I added another couple hrs to the stack.
The ring bands are reduced but still there.

Not Sure where the FLIP setting is located but I don't think I did anything odd that way.
I have attached a document showing the Flats capture setup and results.
I also have a picture showing the Flat FITS file displayed via ASISTUDIO and showing the histogram.

Yes, I realize the Full frame imager is a bit much but would that affect how the Flats are correcting in the main part of the image?
Am I just expecting too much from the flats.
Should the Flats correct most of the image properly.

Thanks for your help on this.
Steve

[admin]

Hi,

the flip control for the ZWO cameras is in the 'Camera Controls' section above the 'Turbo USB' control.

The image that is in the post just above looks like a well exposed flat frame, but the one a few posts further up is very dark. I don't understand why they are so different...

Going back to the first image, the '3d rings' effect - or something similar to it - is there in the image that is processed without flats, so it cannot be a result of the flat correction, so we should forget that line of investigation.

What tool are you using to stack with and have you got the debayer settings correct in it? I have seen some *very* weird results in the past when people try to stack raw images without debayering them. There are certainly some odd purple/green colour artifacts in your image and those colours often show up if the debayer settings are incorrect.

I guess that all comes down to the question : Do the individual frames (no darks, no flats) look OK when stretched a bit? If they look good then the weirdness is from the stacking, if the weird is in the individual frames then it is coming from the camera/optics.

cheers,

Robin

[stbkaiser]

Hi
Thank you for your input on this problem.
I believe I found the issue.
Neighbors lighting.
( I have limited viewing , completely blocked to the east, and anything below 30deg in west)
This is the first time I have tried shooting this low to the south.
The target I'm shooting is somewhat low to the south, right over the neighbors .
They have a nice bright backyard light , on a pole, which they keep on all night. sigh....

My imaging in other parts of the sky with the same setup does not show the issue.
Take care
Steve

[oopfan]

I had the same problem with my new neighbors. City folks escaping urban violence, but then they're afraid of the dark. After two years they finally turned off the light.

Edit: I wish people were just as concerned with light pollution as they are with other types.

Brian

[admin]

Hi,

thanks for reporting back - good to hear that you found the cause, even if it is such an annoying one

cheers,

Robin