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Astrophotography

IC434 - Odd Artifact
Scott Vanaman
1/24/2023 7:51 PM

I was doing the Dynamic Background Extraction on IC434 and saw an odd artifact and was trying to figure out if it is an issue with the data or something else. I have the master Light then the sub after the DBE.


Can you let me know what you think? I can faintly see it in the master light as well.



- Scott V

ASI2600MC

William Optics ZenithStar 73, 0.8x Flattener, ZWO EAF, ZWO ASI120MM Mini Guide

ASIAir Plus

Skywatcher HEQ5 Pro

Daniel Stern
1/24/2023 8:36 PM
Scott, I'm curious to see what others think but my opinion is that it's in the data and just being revealed with DBE. Did you use WBPP? What kind of calibration frames did you use? As a separate matter there still appears to be gradients after DBE. What kind of target image correction did you do? Placing samples can also be tricky because of the amount of nebulosity.

Scott Vanaman
1/24/2023 9:22 PM
At the moment, I did not use any calibration frames. I am in the process of taking them now. I have a ASI2600MC, so since i know the temperature, I should be able to get these shot without issue. Not sure if the flats will work, but I haven't moved the optical train since I took this photo. I was more trying to learn the process of PixInsight that Gary T had shown and figured that it was a better start than I ever got on Photoshop. 

I did use the WBPP on 85x300s exposures to get the master light. Not sure what you mean by the target image correction. I used the division option in DBE, but the subtraction looked the same. I was following the process that Gary had shown, but obviously without the flats, there is still a gradient. It is a lot better than the original image showed

Lou Varvarezis
1/25/2023 8:48 AM

Scott,


That is really weird, my guess is that it's part of the data. The first thing I would try is stack the data using DSS and see if it's still there. WBPP can be a little tricky to use especially during the normalization stage of the data. Sometimes complex gradients can confuse the process if the settings aren't perfect. Let's try to eliminate that from the equation first and move on from there, re-stack with DSS. Also, did you dither between every frame when you collected the data? I am noticing a little bit of "walking noise" on the DBE example you processed.


Some people will argue that dithering is a waste of time however, that couldn't be further from the truth. The astrophotographer's motto is "Dither or Die". Experience will tell you dithering between each sub is the the easiest way to eliminate many problems with your data but it also needs to be done appropriately. If you did dither this time, then you need to increase the aggressiveness because there is obvious walking noise.


It's always a challenge to image such a faint object like the IC 434/B33 under this much light pollution. I am curious to get to the bottom of what caused that huge artifact in the center. Keep us posted. If we can't figure this out before next week maybe you can share your data and we can try to figure it out during our next AP workshop on the Wed Feb 1, 2023. However, I hope we can resolve it before then. Run the data using DSS and post the results.


-Lou

Daniel Stern
1/25/2023 9:11 AM
Scott,
I agree with Lou 100% but it's a good idea to run WBPP or DSS after you include the calibration data. Additionally, my mentors suggest that you include the drizzle option for one shot color. It does add some time to post processing but it couldn't hurt. As a separate issue, when you have multiplicative gradients (vignetting) or differential atmospheric absorption issues (whatever that is - that's what the "book" says) I run DBE twice with the same sample placement. First division and them subtraction.

Dan

Lou Varvarezis
1/25/2023 9:52 AM

Scott,


Dan brings up some valid points. Calibration frames are a must. However, aside from that, drizzle can be very useful if employed while processing. Personally, I don't necessarily think drizzle is needed increase the size of the final image in this particular case however it can still be very useful while processing.


One more thing I should mention, I think you needed to be more aggressive when employing dithering since the walking noise is still evident in your image. What image capture software are you using? Do you know where to adjust the aggressiveness of your dithering?


Drizzle and dither go hand in hand. The other thing you must consider (which Dan mentioned), is drizzle creates a lot of extra files but if you have the space-time (get it, hehehe) go for it. Like I said before, drizzle only works if your dithering. In this particular case I don't think the dithering was setup up aggressively enough but I am still curious to see what will be revealed when it's employed while you process your data. Every single process will take that much longer because the file will be larger so don't think there is something wrong with your computer when you are working on drizzled files.


A good use for drizzle is to use while processing. Drizzle will allow you to increase the size of the image while you're working on it allowing you to get a good look at it the fine detail, then when your done processing it you can resample it back down to normal size.


Let's see what you get when you stack this with DSS. Don't forget to drizzle and fashizzle the nizzle.



-Lou

Lou Varvarezis
1/26/2023 8:19 AM

Scott,


If it still shows up after stacking your data with DSS then I would buy a kit to clean your sensor. Maybe it's something as simple as that?


-Lou

Scott Vanaman
1/27/2023 7:18 AM

I added dark calibration and flat frames. With just the dark frames, the spot is still there. With the flats, the spot was process out when using WBPP. In the flat frames I took, I see a splotch, so there is something in the optical train that I have to get cleaned out.


I attached a screenshot (left to right) of the WBPP with no calibration, WBPP with Darks only, and WBPP with Darks and Flats.


The attached flat (sorry for the green shift, it was just a quick way to view it in PI) shows the splotch.


Thanks for all of the support!



- Scott V

ASI2600MC Pro

William Optics ZenithStar 73, 0.8x Flattener, ZWO EAF, ZWO ASI120MM Mini Guide

ASIAir Plus

Skywatcher HEQ5 Pro

Lou Varvarezis
1/27/2023 8:23 AM

Scott


Good detective work, I think you solved your problem. Now you need to find out where the splotch is and clean it. It's so frustrating to find these artifacts especially if you forget to take corresponding flats. It's happened to me more times than I can remember or willing to admit.


The "splotch" may not necessarily be on your sensor but if it is you can try using this kit to clean it off. CMOS sensor cleaning kit

Good luck, I hope you get all those pesky dust motes out of your optical train.


-Lou

Gary Trapuzzano
1/27/2023 12:10 PM
Hi Scott,

That's great news about being able to calibrate out the artifact using Flats.  I'm always amazed at how much a difference a good set of flats can make during pre-processing.

You probably already know this but, keep in mind when you're tracking down the obstruction in your optical train that the more well-defined the shadow is the closer the dust, etc. is to the sensor.  Shadows on the more diffuse side, like what your artifact appears to be, are likely on an optical element further away from the sensor.

I've attached an article from ZWO about cleaning your camera if you ever need to go this far.  From the looks of your Flat it doesn't seem like you'll need to dissemble your camera (which should only be done as a last resort in my opinion).  I mainly supplied the article because the picture at the beginning of it shows the difference in how dust moots look when they're right on the sensor compared to being on the protective window a little further away.

Keep up the good work.  You're preliminary results are looking very promising.

Gary


Scott Vanaman
1/27/2023 6:03 PM

Here is the photo so far with DBE and Spectrophotometric Color Calibration done on it. This is definitely more than I ever extracted from Photoshop.


Edit: I realize I only did a STF, I still need to get it so that the image itself is stretch. I'll reupload it once I get it done.



- Scott V

ASI2600MC Pro

William Optics ZenithStar 73, 0.8x Flattener, ZWO EAF, ZWO ASI120MM Mini Guide

ASIAir Plus

Skywatcher HEQ5 Pro

Daniel Stern
1/27/2023 7:15 PM
Great. I look forward to seeing the end result. If I can help along the way don't hesitate to ask.

Scott Vanaman
1/27/2023 9:32 PM

Here is the final processed image that I did in PixInsight.


I followed Gary T's tutorial, and that really helped a lot!



- Scott V

ASI2600MC Pro

William Optics ZenithStar 73, 0.8x Flattener, ZWO EAF, ZWO ASI120MM Mini Guide

ASIAir Plus

Skywatcher HEQ5 Pro

Daniel Stern
1/27/2023 10:06 PM
Scott, great result. Well done.

Lou Varvarezis
1/28/2023 7:08 AM

Scott,


Well done, I like how you handled the brightness of Alnitak, that can be challenging and often overwhelms the image but not in your case. Your image has good contrast and does a great job displaying the variation of colors in that area. I know you took a lot of subs -- if you have time, I think the image can benefit from the addition of even more subs, to cut through all that light pollution but that's entirely up to you. There are a few minor details that can still be can be addressed or you can leave it the way it is. Over all, it's impressive how much data you were able to extract from those faint subs you showed us in the beginning. Keep it up, this just keeps getting more fun as you go along.


-Lou

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