Strange patterns in my integrated images.

Jordi · April 2023

Hello,

I need help with my images. No matter what I do, the end result is always weird and ugly. Please some advise about what kind of problem I have here?

The hardware:

- TS-Optics RC 8"
- ASI 294MM Pro
- Antlia 3nm LRGB and SHO filters 31mm unmounted
- AsiAir Plus, Zwo 8 position Electronic Filter Wheel, ZWO OAG with ASI 290mm mini camera
- Gerd Neumann Aurora Flatfield Panel

The circumstances:
- Bortle 9 zone
- Want to image M97

The facts:
- 83 lights 300" H filter; Gain120; Temp. -10 degrees celcius; bin2
- 10 Darks 300", same gain, same temp, same binning
- 30 Flats 55", 24000 ADU, same settings
- 30 Dark Flats 55", same settings

The problem:
My final integrated image shows weird patterns. With all the original data, the g¡final image has the Flat pattern in it. This data is from two days ago, but the same happens with data I took last week. I tried different solutions, but nothing works. Please, let me attach some images from the different approaches I've tried:
- Number 1: the original one, usual settings, original data: Registered with WBPP script, pedestal 400, CosmeticCorrection process. Weighted with NSG, integrated with ImageIntegration with NSG settings.
- Number 2: the same, but with past week's darks (30) instead of this week ones.
- Number 3: no darks, only Flats and Flat Darks (introduced as BIAS in WBPP script)
- Number 4: No Flats neither Flat Darks, only Darks from original session.
- Number 5: No Flats neither Flat Darks, only Darks from PAST session (one week ago).
NOTE 1: I've tried WBPP with NO pedestal at all, and the registered images looked like if I had applied the Binarize process, only black and lots of white dots.
NOTE 2: I've tried with AUTO pedestal, and the result is the same as image Number 1.
NOTE 3: I've regenerated the diseccant tablets and the problem persists.

The Aurora Flat Panel is used at maximum bright. I don't know if it could be flipped filters, but I installed them in the correct direction specified by the manufacturer. I don't want to get them out before I get some orientation.
The RAW light frames look ok, so I think is some problem with the calibration process, maybe some flat issue? Darks and bias look ok. Flats are ugly. Maybe I should try with another light source?

Please, if someone need more information I can provide. Any help and advise will be very appreciated!!

Jordi

Jordi · April 2023

Hi,

I'm attaching here the masters of the same session, and one Dark frame from the session from last weekend.

The differences between darks are great, I don't know why. Last week calibration data was taken inside my house. The calibration data from the newer session was taken outdoors. I think that would be the reason of the Darks discrepancies. I don't have integrated images from last week, because I delete them, but I can do the integration again. It seems that in last week data the problem was more some kind of nebulosity across all the frame, instead of this Flat pattern from this last session.

Thank you for your help,

Jordi

Jordi · April 2023

Dark frame from last week session

Jordi · April 2023

OMG, I've just discovered that my raw subs show the same pattern than my integrated images... May I have a problem with my filters? I'm gonna try to flip the H filter and try. Here you have a STF image, stretched to show the pattern.

BlockHead · April 2023

Hi Jordi,

You have presented me (or anyone trying to answer these questions with quite a bit of work).

My guess is that you have a number of issues and you did not state they were not issues. The way it works in a situation like this isn't to present the "evidence" of different frame type and different situations... but instead to show proofs of what it CANNOT be. Sometimes these proofs are wrong... but by proceeding in this manner there are fewer possibilities for the problems.

As an example... you did not say that you took the darks in the dark. I see so many examples of imagers thinking that their cameras are light tight. It is not so... none of them are. They are sensitive. Even the smallest light leak will cause an issue.

Another thing, you mention the usual settings. Again, I cannot assume that what you *think* is usual is correct. For example, you mention using a bias to correct the flats. But this camera obviously has AMP glow. You have to create matched darks for flats. It could be your exposures are so short they are the same... BUT- some sensors act a little weird for very short darks or flats exposures. Generally a good rule of thumb is to have exposures longer than 1 or 2 seconds. You didn't say this. One thing that contains a lot of this information is the WBPP screen captures. You can generate all of them with a single button press using the diagnostics button.

These strange patterns are well known for this sensor when looking at monochromatic red wavelengths (H-apha). According to some if you are very careful at the pedestal, the darks for flats, the exposure time, how the flats are acquired... etc etc- it is *possible* to get this sensor to perform OK. However, it appears to me that extra effort is required.

Here is a typical discussion with images:

https://bbs.astronomy-imaging-camera.com/d/11841-asi294-mm-pro-flat-field-question/10

So in conclusion..I believe you are doing 2-3 things that are not optimal which do not allow you to properly calibrate out the wacky interference pattern of this sensor. There isn't anything wrong with your filter... you could argue there is something non-optimal about the sensor in terms of its behavior.

-the Blockhead

Jordi · April 2023

Dear Mr. Block,

Thank you for your assistance and guidance. I am aware of the issues with the 294 camera. The only mistake I may have made was taking my calibration frames in a room that wasn't completely dark. There was some light entering through the partially shaded window, although I always cover my imaging rig with black fabric when taking calibration subs. Perhaps there was a leak. I will try taking these frames at night.

Regarding the WBPP script, I only make minor adjustments to the default settings. I change the pedestal when using NB filters (300 or 400) and apply a CosmeticCorrection instance with the Auto setting in the Hot Sigma option. I never feed the script with bias frames, as I understand that CMOS sensors require dark flats with matching values to flats (time, temp, gain, binning). I also know that the 294MM Pro sensor does not perform well with exposures less than 3 seconds. As a result, my H-alpha filter flats are 55" long to achieve 24000 ADU, which I believe is a good ADU level for a flat.

Given these factors, as well as some strange behavior with the OIII filter (a "smoky" background across the entire image), I agree that faulty calibration subs may be the source of my problem.

Thank you again for your help. I will update you on my progress once I have applied some optimizations to my routine.

Best regards,

Jordi

BlockHead · April 2023

Sounds good Jordi.

As a matter of instruction I would say that there are no defaults in WBPP (or really most processes in PI). WBPP in particular is a pipeline and it is script that is configured by the user. They fact that some settings are pre-populated or rely on mathematical principles (such as automatically choosing a rejection method based on number of frames) is not a default and should not be considered as such. It is entirely up to the user to look at each setting and configure it according to their data (and needs). There are many settings most because there are many configurations that people want. Many of these configurations are not applicable to any single user- so the tool seems to have an unnecessary complexity- but any simplification instantly results of howls of displeasure from those it affects.

-the Blockhead

Jordi · April 2023

Dear Mr. Block,

I have made various attempts using different strategies to address the issue I am facing, but unfortunately, none have been successful. I have diligently captured dark frames, flat frames, and dark flat frames in a windowless room, with the entire optical train covered with fabric, except for the camera cooling system. Additionally, I have taken the precautionary measure of covering the camera's LED with tape and turning on the air conditioning to 16 degrees Celsius, which is the minimum possible. I have also captured flat frames with different ADU values along with their corresponding dark flat frames. While the final result is better than the initial attempts, the integrated images are still proving to be challenging to process properly.

Therefore, after much consideration, I have decided that I need to replace my current camera as it is not fulfilling my requirements. I am planning to purchase a 2600mm pro camera and hope that there will be no issues with oil leaks. Nonetheless, I believe that it is a good camera overall and will serve me well. My intention is to use a device that simplifies the process for me: astrophotography has its own inherent challenges, and I do not wish to add the additional complexity of taming a wild sensor.

Sincerely,

Jordi

Jordi · April 2023

Dear Mr. Block,

I would like to inquire if you have an established viewpoint on the ongoing debate regarding the necessity of taking Bias or dark flats with this camera. As per your previous advice, which I have always valued, I believe that CMOS sensors are more susceptible to requiring dark flats. However, I am keen to learn if you hold a similar opinion.

Thank you kindly for your time and consideration.

Best regards,

Jordi

BlockHead · April 2023

I think the rule of thumb is that if the sensor has significant amp glow then matched darks are best. In general most CMOS sensors are entirely well-behaved and can use biases with no issues. It is just a few cameras from a particular popular company that have muddied the water and necessitated this discussion.

-the Blockhead

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