M31 / First light with 2600MC

[AbsolutelyN]

6 minutes ago, gorann said:

Here is my flat run through the Equalize command in PS, which is used by many as a diagnostic tool to find banding and gradient problems and I see nothing there.

Just been digging in the stacked M31 image and flat in PS and I can't find any banding at all.  However I can see it in the Esprit 80 flat I took this morning in PS. So I think it is actually in the file and DBE is just bringing it out much stronger. Looking like nothing wrong with camera though and I just need to alter my workflow to work around it.  

[Spongey]

4 hours ago, AbsolutelyN said:

However I do challenge anyone to process the attached file

Hi AbsolutelyN, I just had a quick go at processing your file for fun, and agree that there is some banding in the background visible after DBE. Once stretched and setting the background to a good level though it wasn't too visible, and adjusting the background (minus stars) saturation helped eliminate it.

It's far from my best work but shows that the problems you have are certainly manageable with careful processing!

Not sure your flats are correcting properly as the very corners are quite dark indeed compared to the rest of the image after stretching. I cropped them out for this process.

Cheers

[AbsolutelyN]

29 minutes ago, Spongey said:

Hi AbsolutelyN, I just had a quick go at processing your file for fun, and agree that there is some banding in the background visible after DBE. Once stretched and setting the background to a good level though it wasn't too visible, and adjusting the background (minus stars) saturation helped eliminate it.

It's far from my best work but shows that the problems you have are certainly manageable with careful processing!

Not sure your flats are correcting properly as the very corners are quite dark indeed compared to the rest of the image after stretching. I cropped them out for this process.

Cheers

That's great, you've done a great job there, prefer it to my version. That file had no flats - it's taken on a rasa 8 so it does not fully cover the chip size. Cropping corners is to be expected.  The banding is manageable but I'm not sure it should be so visible in the first place. Thanks for  taking the time to have a crack at it. 

[DaveS]

5 hours ago, AbsolutelyN said:

Yes agree, maybe I'm digging too deep into the files and you are bound to find artefacts. I do stacking, DBE and star reduction in PixInsight, most of the rest in Photoshop. However I do challenge anyone to process the attached file (M31 stack of 4 hours with no flats) and not find the banding in the image - it's pretty prominent once you run a DBE and start to work on the image. 

Temp was -10 but I got the same at -20 a few days earlier so don't think it's temp dependant. I'm using 2 min exposures form Bortle 5. 

integration4.xisf 298.95 MB · 2 downloads

I would have had a go in AA7, but that file looks PI only. Don't have, and don't want, PI

[Spongey]

That's very kind, thank you!

47 minutes ago, AbsolutelyN said:

That file had no flats

This explains a lot! But yes, your star shapes aren't the best around the periphery of the frame for sure, do you have the backfocus 100% nailed in? I feel like more of the image should have round stars than it does...

Compared to Goran's excellent M31 with the same scope + camera (although these were taken from the .jpg so won't be entirely accurate):

 

Edited November 11, 2020 by Spongey

[Nikolas74]

Excellent image! 👍

[AbsolutelyN]

23 minutes ago, Spongey said:

That's very kind, thank you!

This explains a lot! But yes, your star shapes aren't the best around the periphery of the frame for sure, do you have the backfocus 100% nailed in? I feel like more of the image should have round stars than it does...

Again that's the rasa, it's tricky to get good stars with 4/3 sensor, never mind aps-c. It was just a test shot so I've not yet spent time trying to tweak the back focus and centre camera and doubt I'll ever get it perfect. How camera attaches is not great - each time you remove or rotate the camera it ends up in a different position and impossible to centre it perfectly. With my 1600mm I spent hours getting it as good as possible and then dared never touch it again ... 

Edited November 11, 2020 by AbsolutelyN

[gorann]

43 minutes ago, AbsolutelyN said:

Again that's the rasa, it's tricky to get good stars with 4/3 sensor, never mind aps-c. It was just a test shot so I've not yet spent time trying to tweak the back focus and centre camera and doubt I'll ever get it perfect. How camera attaches is not great - each time you remove or rotate the camera it ends up in a different position and impossible to centre it perfectly. With my 1600mm I spent hours getting it as good as possible and then dared never touch it again ... 

I fully agree! I love what the RASA 8 can do, except for allowing tilt adjustment. The ASI2600 has a tilt plate but on the RASA 8 it is only accessible after unscrewing the camera which makes it rather useless. Someone should invent an acceible til adjustment to put between the camera and this scope! The new dedicated Artesky connection (although still no tilt adjustment) that I just received seems a bit less flimsy than the one that comes with the RASA, but I am clouded in so I cannot report on its performance.

Edited November 11, 2020 by gorann

[wimvb]

On 10/11/2020 at 20:34, AbsolutelyN said:

 

This pattern reminds me of newton rings. And since newton rings are caused by thickness variations in a thin film, it may very well be that there is a natural thickness variation somewhere in the light path. lThis can be a cover glass that is not perfectly flat, or a deposited film on the sensor itself. Maybe even thickness variations in the microlens layer. Since it also shows in the flats, and because flats can remove it, it must be optical in origin, not electrical.

I'm certain that you can adjust your workflow to minimise the banding, but that will be limiting your process and your final results. As always: try to eliminate unwanted artefacts as early in the workflow as possible, i.e. by using flats.

To lessen the impact of the bands during processing: use a mask when you saturate the colours in the galaxy. Or in PS speak: use layers. (Did I just mention PS? the horror 😬)

[wimvb]

I had a go at the data. As already noted, the banding starts to become visible after DBE, or, in my case after colour calibration. I check the "normalize" box in DBE correction, which maintains the median background (including colour imbalance).

Here's my result. I couldn't completely remove the vignetting, and had to resort to scissors (crop). Flats are a must, in my opinion. I also kept the saturation down. Following my own advice, I increased the colour saturation in the galaxy with the help of a mask, and reduced the saturation in the background with the same mask inverted.

[AbsolutelyN]

9 hours ago, wimvb said:

This pattern reminds me of newton rings. And since newton rings are caused by thickness variations in a thin film, it may very well be that there is a natural thickness variation somewhere in the light path. lThis can be a cover glass that is not perfectly flat, or a deposited film on the sensor itself. Maybe even thickness variations in the microlens layer. Since it also shows in the flats, and because flats can remove it, it must be optical in origin, not electrical.

I'm certain that you can adjust your workflow to minimise the banding, but that will be limiting your process and your final results. As always: try to eliminate unwanted artefacts as early in the workflow as possible, i.e. by using flats.

To lessen the impact of the bands during processing: use a mask when you saturate the colours in the galaxy. Or in PS speak: use layers. (Did I just mention PS? the horror 😬)

That's absolutely fascinating thanks - love your rendition of the image too. 

[kirkster501]

Wim's version of the picture is magnificent.  One of the best M31 I have ever seen with great colours, detail and the outer halo shining which is so easy to clip out when trying to get the background dark.

Just shows the data was there all along.  Like a marble statute encased in the mined, raw stone.  It takes expertise to chip away at that block of stone to reveal the statue.  Same here.  IMO the biggest problems people make is overdoing the noise reduction and oversharpening/HDR/Deconvlution.  Can destroy the picture and make it look "weird" if overdone.

One thing I'd like to see, with my version too, is the addition of Ha data to get the HII regions to pop - which the OSC CCD's don't capture that much of without a filter.  You could run the colourmask script on red then use that as a mask, edit the mask so as only the Ha regions are revealed and then use curves to enhance the red a little bit.

[tomato]

12 hours ago, gorann said:

I fully agree! I love what the RASA 8 can do, except for allowing tilt adjustment. The ASI2600 has a tilt plate but on the RASA 8 it is only accessible after unscrewing the camera which makes it rather useless. Someone should invent an acceible til adjustment to put between the camera and this scope! The new dedicated Artesky connection (although still no tilt adjustment) that I just received seems a bit less flimsy than the one that comes with the RASA, but I am clouded in so I cannot report on its performance.

The QHY 268c comes with a built in tilt adjuster which is accessible on the RASA, the trouble is it takes up 6mm of the available back focus so I am struggling to get this right, never mind compensate for the squidgy Celestron adapter plate.

[tomato]

44 minutes ago, kirkster501 said:

Wim's version of the picture is magnificent.  One of the best M31 I have ever seen with great colours, detail and the outer halo shining which is so easy to clip out when trying to get the background dark.

Just shows the data was there all along.  Like a marble statute encased in the mined, raw stone.  It takes expertise to chip away at that block of stone to reveal the statue.  Same here.  IMO the biggest problems people make is overdoing the noise reduction and oversharpening/HDR/Deconvlution.  Can destroy the picture and make it look "weird" if overdone.

One thing I'd like to see, with my version too, is the addition of Ha data to get the HII regions to pop - which the OSC CCD's don't capture that much of without a filter.  You could run the colourmask script on red then use that as a mask, edit the mask so as only the Ha regions are revealed and then use curves to enhance the red a little bit.

I can only echo Steve’s and others’ posts, this is a phenomenal M31. I have 3 hrs of data using essentially the same kit and conditions, but I cannot get a processed result coming anywhere near this, awesome job.👏

[gorann]

11 hours ago, wimvb said:

I had a go at the data. As already noted, the banding starts to become visible after DBE, or, in my case after colour calibration. I check the "normalize" box in DBE correction, which maintains the median background (including colour imbalance).

Here's my result. I couldn't completely remove the vignetting, and had to resort to scissors (crop). Flats are a must, in my opinion. I also kept the saturation down. Following my own advice, I increased the colour saturation in the galaxy with the help of a mask, and reduced the saturation in the background with the same mask inverted.

Very skilful processing Wim! Cannot be done better and it is now among the best M31 images, as already said here.

However, I notice one thing unrelated to the processing: there are starspikes, which I found can be avoided with curved cable management, as I did after seing those spikes in my M31 data. This is how I arranged my cables (shaped by taping them to a curved steel wire). Takes away all spikes.

[gorann]

1 hour ago, tomato said:

The QHY 268c comes with a built in tilt adjuster which is accessible on the RASA, the trouble is it takes up 6mm of the available back focus so I am struggling to get this right, never mind compensate for the squidgy Celestron adapter plate.

Yes the ASI2600 also has a tilt plate but I think it would be very difficult to reach the screw heads to adjust it while it is attached to the RASA. I think I may have just invented an alternative made by a folded thin aluminium-sheet cut out from a beer can. It can be pressed in between the holder-ring and adapter (Artesky or Celestron). Clouds prohibit me to test in right now.

[tomato]

Hi Goran, 

So you are using the thin aluminium as a shim under the plate?

[gorann]

7 hours ago, tomato said:

Hi Goran, 

So you are using the thin aluminium as a shim under the plate?

yes, and rotate it around until I get the right corner lifted and all stars round. If the thickness is not enough I just fold it a bit more. I hope it could be quick and simple, maybe have the handle inside a rubber band around the camera. That is my theory at least - cannot test it yet.

[AbsolutelyN]

1 minute ago, gorann said:

yes, and rotate it around until I get the right corner lifted and all stars round. If the thickness is not enough I just fold it a bit more. I hope it could be quick and simple, maybe have the handle inside a rubber band around the camera. That is my theory at least - cannot test it yet.

Let us know how it goes. I always felt it was centring and getting precise back focus causing star sharp Issues but I guess that was all I could control. Hope it works.

[AbsolutelyN]

again please let us know how the new adapter performs, almost bought one a few months ago but no stock. 
I got my best stars with 1600mm with starizona filter adapter and a baader 0.3 metal spacer

[gorann]

To me it has been kind of a random process especially with the ASI2600 and the flimpsy Celestron adapter - some nights are better than others dependent on how it happened to be positioned. I hope the Artesky will prove a bit better. At least it does not have the soft pads on the back side and it wobbles a bit less when it comes to center it. For my ASI1600MM I use the Baader filter slider and it is a bit more repeatable and then also the chip is smaller.

Edited November 12, 2020 by gorann

[gorann]

1 hour ago, AbsolutelyN said:

again please let us know how the new adapter performs, almost bought one a few months ago but no stock. 
I got my best stars with 1600mm with starizona filter adapter and a baader 0.3 metal spacer

To me it has been kind of a random process especially with the ASI2600 and the flimpsy Celestron adapter - some nights are better than others dependent on how it happened to be positioned. I hope the Artesky will prove a bit better. At least it does not have the soft pads on the back side and it wobbles a bit less when it comes to center it. For my ASI1600MM I use the Baader filter slider and it is a bit more repeatable and then also the chip is smaller.

 

[tomato]

When I can get access to @Tomatobro’s workshop I think we will turn up a RASA adapter plate for the QHY268c, which will bolt directly onto the camera’s tilt adjuster. This will enable precise back focuser spacing, eliminate  the soft backing material and sloppy centre alignment of the Celestron adapter, and allow use of the QHY adjuster.

Just need the R number below 1...

[John Nodding]

Just had a gander at the full res image......AbsolutelyN-ailed it!  Simply stunning! 👍

Noddy