Light Pollution Issue

@rockinrod Rod, did you use any flats and, if you did, were they taken with the same filter? There are a lot of dust bunnies in your image which seem to indicate either no or incorrect flats. I'd start with ensuring that that's OK before pursuing further attempts to correct for the light pollution.

Wouter

@wvreeven

Yes, I used flats and bias frames, same Gain of 120 (unity gain) for my ZWO. There was a crap load of pollen on the collector plate I saw this morning. That may be some of it...

I also tried Astro-Flats which is an add on in my Photoshop 2021.

Thanks!

@rockinrod So, apart from taking another look at your flats and making sure they are correct, I don't know what to do. Removing light pollution depends on the smoothness of the background and with those dust bunnies the background is far from smooth. Are you using a OSC? Is the peak of the histogram far to the right but not clipped? Even with dirty optics, proper flats should remove those dust bunnies.

 This is the same filter, IR-Cut the night before on M81, 120 second exposures...Quite a contrast. Both in the northern sky.

Only difference is I took 240 second subs on M101, and got the foggy stuff...I took my flat frames outside early morning with a T-Shirt, using the same Gain settings, and I had the Means set between 18,500-21,000 as recommended.

@wvreeven

I seem to forget what OSC is...I'll check the histogram...I just ran everything thru again. I've tried several types of integrations, all get the same result. This is before any processing at all. Just so you can see what Im seeing.

@rockinrod Hi Rod,

OSC = One Shot Color camera. I assumed you were using one but now I am not so sure anymore.

Very strange that the flats don't work on M101 while they do on M81. Could you upload a few raw flats taken for both sessions to

https://upload.astropixelprocessor.com

in a directory called rockinrod_flats? Please use upload1 for both username and password.

Thanks, Wouter

Posted by: @wvreeven

@rockinrod Hi Rod,

OSC = One Shot Color camera. I assumed you were using one but now I am not so sure anymore.

Very strange that the flats don't work on M101 while they do on M81. Could you upload a few raw flats taken for both sessions to

https://upload.astropixelprocessor.com

in a directory called rockinrod_flats? Please use upload1 for both username and password.

 

Thanks, Wouter

Oh drat, of course. My brain was so rattled I'd forgotten...I used an ASI294MC Pro cooled camera, yes, OSC...I'll see about uploading those files...

Thanks

For some reason that upload page does not like my login info...Using the same thing I logon on to ask my questions. To get it...Still trying to get in.

I changed my password, then tried to use it on the upload page. It's not working. There is also an image of a locked Lock in the Password Field. Not sure if that means anything

Hi Rodney, you can't use your own login there. Please use upload1 as the name and upload1 as the password (both are the same).

@vincent-mod

I got ya. I misunderstood the login info...I uploaded 8 files there, 4 for M81 and 4 for M101...I used the same flats, with the same 120 Gain...

Wow, I think I see the problem...Nasty looking flats, yet why didn't it affect M81...That's a mystery

@vincent-mod

Got those files uploaded, but I can already see my flats stunk...!I'm redoing those now, and some new darks. I also used my CLS filter last night, at 6 minute exposures...Helped considerably but it needs more exposure time and data for this particular galaxy. Thanks for all your help!

I

 I'm about 50% of where I want to be with this....

@rockinrod Thanks for confirming that my initial suspicion about bad flats was correct!

@wvreeven

I'm trying to correct this now...One thing I found, at least on this particular object...The more flat frames used the worse it looks..I just ran everything thru 30 Lights, 30 Bias, 30 new Darks, and just 5 Flat frames...The result is much better...I think I will invest in one of those Flat frame Light panels which sits on top the scope. Stop using the T-Shirt method...

 This is with 5 flats...Big Diff...!

@rockinrod Wow that indeed is a big difference. Are you taking all flats at the same exposure time or do they vary?

@wvreeven

Same..I'm using nebulosity...Setting the gain the same as the lights, the "Means" values set at 21,350 at an exposure time of 0.04 sec. The problem I'm seeing here is using this 50Watt LED light is not uniform across the OTA...Causing Vignetting and for some reason this hazy appearance...

@rockinrod Could there be internal reflection in the telescope tube? If yes then that will change the properties of the optical system leading to unusable flats. Also, 0.04 sec is VERY short. Many modern cameras have rolling shutters with shutter speeds in the order of milliseconds. This may lead to uneven read out times for the pixels causing a lot of issues. You may want to aim for exposure times of at least a second. This can be easily achieved by adding more layers of white t-shirt to dim the light source.

@wvreeven

I used two layers this morning. I saw a video on Flat Frames from one dealer, maybe OPT, maybe Starizona, can't remember, which said to shoot for a 19500 to 21500 Means number. So that's basically what I've been doing. Either moving the light closer or further away.

I know the Bias frames are very fast...I set the ZWO at .000032

I have an OSC ZWO...

I'm not sure how one would check for this internal reflection. First time I've heard of this. I used a Glare shield on it like always..

@rockinrod Take the camera off the telescope and shine the light source for the flats in it. Then look at the other end and try to determine of there are reflections could be a way to check.

@wvreeven

I'll give it a shot.

@wvreeven

Scope is tight as a drum...I sent this in to Starizona for service and collimation last year. They worked it over pretty good too...

@rockinrod The point is to give it a look, not a shot 😉

@rockinrod Yeap that looks really well! So, it's not internal reflections then!

@wvreeven

I've been doing this hobby for better than three years now, and this is the first time I've seen this problem, this bad...

I just opened up my ZWO and checked the desiccant tablets and cleaned the sensor cover...Had some dust particles and what appeared to be some sort of film on it...Cleaned it off with some lens solvent and lens papers...I may do some new Flats since I did this just to see what happens.

I set up for flats again using Astro Photography Tools. I have a 14-Bit camera so I entered the ADU number, 8192 and ran it...Seems to look much better than Nebulosity's...

I'll stick with this method and see how it works on other objects..