In need of help with flats, can't solve the issue.

[xEOIx]

Hi all, 

I have been having issues with calibrating my images for several months now. I can't seem to isolate the issue, and I am in need of some help. 

My equipment: 

AT72edii with AT2FF field flattener

QHY294m, QHY163C, CFW3 filterwheel and OAG. 

Filters: Baader LRGB, Chroma Ha/Oiii 3nm. 

Software: DSS for stacking (can try in PixInsight too)

Things I know are not the problem: Field Flattener, OAG, camera?

Things I cannot totally rule out: can the scope be an issue? I don't think my filters are an issue since rotating the camera yields the same flats being taken (I tried that on the Oiii, haven't tried it on the others), Filterwheel

Here are some sample flats that are already stretched in PI, let me know if I should post tifs or maybe even the stacked images that show insufficient calibration. Thank you in advance.

[PeterCPC]

But you don't actually say how you are taking the flats.

[michael8554]

As Peter said.

Are you just pointing at the dawn sky, cos they look like clouds !

Also some have a hint of shutter shadow ?

Michael

[tooth_dr]

I’ve had flats like that when I took them in the daylight. Are you taking them during day and having possible light leaks?

[wimvb]

That edge at the bottom looks suspiciously similar to a reflection off the oag. Pull the oag stem a little further out and see if it changes. Also, what filter size do you use? Unmounted filters may have edge reflections that can mess up flats.

[The Lazy Astronomer]

The 294 mono sensor is known to create some 'interesting' narrowband flats, but lrgb should look normal.

I'm having a similar issue at the minute with my asi294mm - I have some flats (which I have used successfully on 2 previous images) which are now not fully correcting the lights. Going to experiment a bit this afternoon to try and figure out why. 

[ollypenrice]

These are not credible flats. The patterns of light and dark cannot possibly be created, as they should be, by collecting light as the telescope collects it and the camera records it. Something else is getting in there and creating the patterns we see, so we need to know everything about every light source ending photons onto your chip. That means a precise description of your method, including any sources of ambient light.

Olly

[xEOIx]

Sorry, I should have given more details but was afraid my post would be too long. These flats were taken using an ipad screen with a white background. They were in my bedroom which was as dark as possible, but there was still some light from as it was not totally night time.

I have tried to reduce any potential light leak by putting a towel on my setup, but unfortunately I couldn't think of a good way to cover the connection between the camera and filter wheel. In the past I had taken flats using the dawn sky and compared them with the ipad and I thought (key word on thought) that they seemed to be the same. I also have an EL panel coming in today so I can do more tests with that. 

All of these flats were taken with the oag fully retracted. 

edit: Many of these flats were under 2 seconds, some of them were under 0.1 seconds, especially for LRGB. Here is a link to a google drive with some of the raw files (5-10 each). https://drive.google.com/drive/folders/18rY_CqSxqStFk8JGYmhAXvON5OmhDv-l?usp=sharing

Edited June 26, 2021 by xEOIx
important information

[xEOIx]

I think it may be useful to include single light subs taken. Here are the Ha and Oiii stretched with STF in PI. I have also included Ha and Oiii fully stacked and calibrated using darks, flats and dark flats. Thanks. 

[ollypenrice]

If the OAG is fully retracted I presume you're not using it. In that case why not remove it? It's a very likely source of unwanted reflections and shadowings.

Olly

[vlaiv]

Very strange thing those OIII flats.

Same pattern appears in both Ha and Ha flats, and Oiii and Oiii flats - yet Ha calibrates fine while Oiii does not.

Here are uncalibrated OIII and Ha subs binned to oblivion (x16) to raise SNR and show pattern

Here is calibrated Oiii:

Flats over correct.

I suspect that there was some sort of light leak when shooting OIII flats.

Both Ha and OIII do have very strange flats indeed - but I would not worry too much as long as it calibrates out properly.

 

[xEOIx]

4 hours ago, ollypenrice said:

If the OAG is fully retracted I presume you're not using it. In that case why not remove it? It's a very likely source of unwanted reflections and shadowings.

Olly

I am using the OAG, I just retracted it to test the flats and rule it out. I don't think it was leaking light in this case since I have the whole setup covered anyway. I think it may be as the post above suggests, some kind of light leak from between the filter. Might have to find a way to fasten a gasket on the QHY filter wheel. Something like how ZWO gives. Thanks for the reply

[xEOIx]

3 hours ago, vlaiv said:

Very strange thing those OIII flats.

Same pattern appears in both Ha and Ha flats, and Oiii and Oiii flats - yet Ha calibrates fine while Oiii does not.

Here are uncalibrated OIII and Ha subs binned to oblivion (x16) to raise SNR and show pattern

Here is calibrated Oiii:

Flats over correct.

I suspect that there was some sort of light leak when shooting OIII flats.

Both Ha and OIII do have very strange flats indeed - but I would not worry too much as long as it calibrates out properly.

 

yes, I had seen the pattern was similar to the light pattern, I was just confused as to why it wouldn't calibrate out. even the Ha was not a perfect calibration, as it looks like the center is a bit darker. It was just weird since my flat with a clear/L filter shows characteristics that each filter has to some extent. the Green, blue and Oiii have the bottom lines and vertical columns, whereas the red and Ha have that small little curve on the right side. So the patterns in both lights and flats seem wavelength dependent. People have been reporting similar weird flats and issues with the 294 series cameras I guess. 

Thank you so much for the reply, I really appreciate that you took the to bin and look at the images more closely. Also, I love that you are using ImageJ/FIJI, never thought I'd see that on an astronomy forum, what do you use it for? 

[vlaiv]

1 hour ago, xEOIx said:

Also, I love that you are using ImageJ/FIJI, never thought I'd see that on an astronomy forum, what do you use it for? 

I use it to all things astro related as it is such a versatile tool. Even have couple of plugins that I wrote for it to do various things like background removal and such.

[Richard Shagam]

I've been having similar problems with the following equipment:

AstroTech AT72ED II
AstroTech Field flattener
Optolon L-eXtreme filter
ASI294MC Pro camera
 8" Amazon Fire Tablet

My flats look suspiciously similar to those posted by xEOIx.  I'm making my flats with an 8" Fire Tablet using the 'White Screen' Android app and a sheet of white printer paper to further diffuse/attenuate the light.  The dew shield is extended, and I place the tablet on top.  Using the APT flat tool, my exposures for 20,000 ADU come out to 9 seconds.   I don't think I'm getting ambient light leaks.  I get the same results whether or not the room is darkened.  I've also had similar results with a larger USB artist's tracing tablet  panel I purchased on Amazon.  Frankly, I'm getting way better results without using flats in my processing.  That is to say, using the flats gives me garbage!

Is there any more insight to this problem?  Is it in the 294?