533mc Pro - Reddish Artifacts

AymenAissa

Hi everyone,

I’m experiencing an issue with my 533mc Pro camera and could use some advice. When I take RGB pictures using the Antlia Quadband filter, I notice two large reddish areas in my images. This problem persists even in my flats, and the WBPP process doesn’t seem to eliminate these artifacts.

Interestingly, the same reddish areas appear when I shoot without filters as well. However, when I switch to narrowband (NB) imaging, these artifacts become much less pronounced.

I’ve tried all sorts of gradient removal techniques, but the reddish areas just turn white and the background remains unclean.

Has anyone encountered a similar issue or have any suggestions on how to address this? Any feedback would be greatly appreciated!

Thanks in advance for your help.

AymenAissa

Anyone to help pls !!

Astrop

You've confirmed it with your flats and unfiltered, does it appear in the same area when imaging a different location in the sky. What optics are you using?

AymenAissa

Astrop it happens all the time with all the filters and all my scopes ( 190MN, FRA400 and with reducer at 280mm) but it’s more pronounced with the L Quad.
My understanding is that the flats will cancel any artefact, however in my case it seems the flats are overcorrecting the image and hence the reddish regions appear white post stacking.

Tech@ZWO

AymenAissa Could you share some flats frame and light frame that can not be calibrated to me? BTW, if you rotate the camera only, will the pattern change?

AymenAissa

Tech@ZWO This is from yesterday’s session shooting the M31 (300s single frame). I have also rotated the camera however the pattern seems to be constant. Correcting these artefacts with flats will convert them from red to white.
I’m keen to know whether this is a standard and normal issue with 533MC Pro, and in this case how to remediate it.

Tech@ZWO

AymenAissa Could you share some flats, bias, and light with me via google drive or other cloud drives? i will try to calibrate it, thank you..

AymenAissa

Tech@ZWO I have uploaded the lights, flats and dark flats for M45 on the drive.
https://drive.google.com/drive/folders/1VCKhvRMuXXcQrE65ChEwHEO4VlvbU6pf?usp=sharing

AymenAissa

Tech@ZWO I have uploaded the lights, flats and dark flats for M45 on the drive.
https://drive.google.com/drive/folders/1fUmqBtxOBRKPaqnNRxJbhStprQ-lvfvd?usp=sharing

Astrop

Calibration with flats should not change the colour to white. Something in your workflow is wrong. The data including your calibration files is usually treated as mono data until you calibrate, then your set pixel debayer pattern converts the data to colour.

If it's turning white, your flats maybe too bright, are you using the auto expose function?

AymenAissa

Astrop I use WBPP for stacking so i assume the workflow is standard.

Astrop If it's turning white, your flats maybe too bright, are you using the auto expose function?

Yes, using the auto expose on Asiair and trying to keep the histogram at 32-33k.

Astrop

AymenAissa Yes, using the auto expose on Asiair and trying to keep the histogram at 32-33k.

If you're using the asiair auto flat exposure you havent got full control over where the histogram peaks other than altering the flat panel brightness which will move it about (you are using a flat panel right? (Like those affordable LED drawing tracing panels)). 32-33k peak I believe is half way, that's way too bright.

My last session at F6 my peak was only an eighth across from the LHS of the histogram, I thought it was dim so raised the brightness of my panel so the peak was more like a third across from the LHS. In either case the auto exposure worked itself out to 10s per flat. I neednt had worried, the dim one calibrated perfectly.

I suspect you may be overexposing your flats. Dim your light source down with diffusing material.

w7ay

Astrop 32-33k peak I believe is half way, that's way too bright.

Take a look at the Max ADU value. If it is saturated at or near 65535, it is indeed too bright (clipping).

However, if the light falloff from your OTA is small, the difference between max ADU and average ADU can be quite small, and there is no problem driving the gain and exposure time of the flats to over 40000 (16 bit scale), and can be advantageous (fewer flat frames needed to attain the same averaged standard deviation).

Yeah -- never use "auto" anything with ASIAIR.

Chen

AymenAissa

w7ay Hi Chen !! I have attached a link to my lights and flats. Could you please have a look and let me know what went wrong with these files.
https://drive.google.com/drive/folders/1fUmqBtxOBRKPaqnNRxJbhStprQ-lvfvd?usp=sharing

iosif

AymenAissa

Your flat at 330.0 ms are too short exposure. Dim the light, to have longer time and exposure between 23000 --- 31000 ADU
As i see you don't have in sent file to google drive dark at 300 s.

Solve this and then can see.

w7ay

AymenAissa Could you please have a look and let me know what went wrong with these files.

What are you using as a flat panel?

I sent one of your flat files and one of your flat dark files to process into a Master Flat in AstroPrixelProcessor and got this as the master flat's histogram:

Notice that with the exposure value (exposure time x camera gain) that you are using, the green channel is swamping your data (i.e., the large ADU is coming from the green channel), and your red channel response is so low that it is clipping at the low end.

That clipping is causing the red part of the flat calibration data to not be able to correct for the lower level red in your light frames. You need to use a flat source that has enough overlap to the SII and H-alpha regions of the spectrum. The blue (OIII and H-beta) is also a little low, but at least not clipping, so using more flat subframes should be a workaround.

Are you using a cheap LED tracing panel as the flat source? If so, that is your problem -- the red LED in those panels do not overlap the red channel (H-alpha) of your filter. There are better panels that are built with "white" LED, which have a more continuous spectrum than separate R, G and B LEDs. But if you plan on doing narrowband imaging, do yourself a favor and get something that is designed for use as a flat source. Like the EL panels from Gerd Neumann, or broadband white LED panels from Geoptik. An incandescent source (like a halogen bulb) should work too (through many layers of translucent plexiglass).

If you are not willing to build or buy a real flat source, you can try using a sky flat at dawn.

The other thing that you can try (and you might need that for narrowband imaging, even with a sky flat) is a bunch of red plexiglass or red gel filters (like what professional lighting people use for stage lighting) over your current panel to suppress as much of the green as possible so that you can then use a longer exposure to bring the red response up from being clipped. E.g.,

https://www.amazon.com/lighting-gels/s?k=lighting+gels
https://www.amazon.com/Translucent-Acrylic-Plexiglass-Sheet-Thick/dp/B07K9P8LSK

Chen

AymenAissa

w7ay thanks Chen for the thorough response. The flat panel is indeed cheap (20$) but even when using the sky at dawn the red pattern is visible. I will anyways follow your instructions and see how it goes.
Otherwise, do you think the red pattern in the light image is normal ?

wvreeven

AymenAissa Is the red channel clipped even if you dim the sky with a white t-shirt and take flats of 1 to 2 seconds?

Astrop

I use those cheap white LED tracing panels, they work perfectly fine, and I always auto expose with the asiair. But I set the panel on its dimmest setting and still diffuse with layers of plastic, flats with OSC camera and lum filter end up around 3-4s long, mono and NB filters 10s long.