what normally causes this!?

[Rustang]

5min subs stacked. The strange thing is I included flats and it didnt take out the sensor marks!? but I'm more concerned about what the other weird gradient issues be something with the deep sky stacking software!?

Edited September 6, 2020 by Rustang

[tomato]

I don't know if you are using a cooled camera, but I had similar dark spots on a CMOS camera retro fitted with a Peltier cooler. There were caused by water/ice particles falling onto the sensor window, particularly when imaging close to the zenith. I fixed the problem by running the camera a bit warmer, it didn't need to run super cold, just be kept at a constant temperature. Flats won't remove them unless they were there at the time the calibration frames were taken.

The gradients I see in the image are quite common in my pre-processed stacks, usually due to local light pollution, poor atmospheric conditions, or the moon being up and/or too close to the target. If not too severe, they can be dealt with in post stack processing, most imaging software packages have a tool or add on for this. 

[Rustang]

I'm using a DSLR, this particular one is a full frame Nikon, not cooled. Its enclosed in a field flattener and the inside a refractor so hopefully not anything landing on the sensor, just crud that's all ready on there! I use the RC astro gradiant remover plug in which in normally really good but it's not getting rid of the strange red  ring on the left or the right hand vertical lines. Maybe the 5min sub is to much for the sensor heat wise and causing this!? 

Edited September 6, 2020 by Rustang

[Seelive]

Any sign of the anomalies on any of the individual images?

[Rustang]

44 minutes ago, Seelive said:

Any sign of the anomalies on any of the individual images?

Il have ago at stretching a couple of subs and have a look to see if there is. 

[Rustang]

So it does appear to be on the individual subs, could it be a heat problem from the sensor!?

Its a really bad stretch but enough to show whats going on.

 

[Seelive]

Should have also asked if stacking with and without flats makes any significant  difference to the final image.

What instrument were you using for the images?

[carastro]

Stacking images without flats is never going to give a decent result. 

I think your flats haven't worked.  The other artifact, could be clouds, sky gradients or even the effect of the flats not working properly.

We need to find out what you are doing to create your flats.  I made the same mistake when I first started and was over exposing the flats so that they were completely useless. 

Carole 

[alacant]

8 hours ago, carastro said:

We need to find out what you are doing

+1.

With no information, all we can do is guess. If you post -links to- example light, flat, bias and dark frames, or whatever you used, and an explanation of how you produced each, we'd be able to nail it.

Cheers

[carastro]

We don't really want to see the flats as it is difficult to tell looking at a posted flat without being able to stretch it, but we need to know your method of doing them.

Carole 

[Rustang]

Sorry guys, only just seen your replies. So I have produced my flats in the past using a laptop screen and have also tried doing it through a white T-shirt over the scope outside. While I type this though I have just realised that was for my old set up with the 130 PDS, the image above was taken with my SW80ED, I wasnt supposed to really attempt to image M33 (the above image), it was the first night of testing out going completely laptop controlled and guide for the first time. It went so well I thought sod it and managed to get an hours worth of data before the clouds came in. In my haste to edit I threw in flats from last year that were taken with the 130pds but the data of M33 was taken with the SW80ED frac so Im guessing thats not going to help!?

Early this year I got an LED light drawing pad to make new flats and that has worked really well with my last image of the heart nebula. You can see in the single 5min sub though that the left hand red ring is present and the line running down the right so could be as you say clouds or sky gradients etc. If it is sky issues then would the correct flats get rid of this!?

 

Darks and Bias taken the normal way on the same night although not that many!

Edited September 8, 2020 by Rustang

[Seelive]

Using the correct flats will certainly improve matters considerably but flats will only correct errors introduced within the optical path, they won't correct any issues arising from the sky itself.

[carastro]

Using the wrong flats of course is not going to work Lol.

When you use your white screen or the sky, you need to make sure that the flats are exposed to the correct value.  the histogram needs to be approx 1/3 to under /12 way from the left, or around 22,0000 - 25,0000 ADU depending on your camera.  If it's a DSLR, you will have to look at the histogram.  If the flats are too bright they won't work at all.

Carole  

[Rustang]

Yeah, I was to hasty to stack the data and wasn't thinking 😊 I'm going to re do my flats with the new set up and see how it goes. 

[Rustang]

So my new flats have worked in regards to removing the sensor marks but like you said, not the other issues which could be clouds or something else I couldn't visible see in the sky. I have a question though in regards to how a stacked file should look in a folder! If you look at the attached image you can see 3 stacked files that look crazy and Ive not had them look like that before. They don't open in photoshop like that, they appear to open as the normal image ready to stretch but what does this mean is going on!? I have done a quick stretch of the new stacked file with better flats, somethings definitely up and it would be really good to figure out if this is sky issues or equipment!? It looks like some kind of strange lens flaring, I couldn't see any visible clouds but could clouds cause this!? or over heating of the camera sensor!? The moon was out that night too, not full though but I would only expect a normal gradient of light coming in on one side not whats showing below!

Edited September 9, 2020 by Rustang