Coathanger, the full half hour...

[ollypenrice]

34 minutes ago, Catanonia said:

That is why I went for the smaller ZWO183MC with the much smaller pixel size. No such issues for me and my RASA 8 and getting very good resolution / sampling.

I can see the simplicity of sticking to a smaller chip size but, for me, 400mm isn't a focal length I'd instinctively use in search of high resolution. We're at 1.9"PP which won't be very seeing dependent and makes the system a good compromise between speed  (flux per pixel) and resolution. On the other hand the RASA should have the aperture to deliver higher resolution, certainly, when you have the seeing. Your sampling rate of 1.24 is, in principle, a viable galaxy imaging resolution. I'll be more than a little interested to see what you get on small, high res targets. The idea of just swapping the camera to go from widefield to high res has to be appealing!

Olly

Edited September 2, 2021 by ollypenrice
clarification

[wimvb]

2 hours ago, ollypenrice said:

The idea of just swapping the camera to go from widefield to high res has to be appealing

Then the ASI294MM should be very interesting. It has about the same sensor size as ASI1600/kaf8300. When it was released it was hard coded as bin 2x2 with 4.6 um pixels, giving it 0.95"/p at 1000 mm. But since then, ZWO have released an updated driver, unlocking the 1x1 state (but with less impressive specs on paper). So now the camera can be used with 0.95"/p at 500 mm and 0.95 "/p at 1000 mm.

[AKB]

On 01/09/2021 at 09:10, ollypenrice said:

a smaller chip would have been performing well some time ago

I do note that the documentation for the RASA 8" says "~22mm diagonal is optimal", but I suppose that you simply had to test their statement  "...can also be used with larger sensors up to 32mm diagonal, ... though some compromise must be expected at the image periphery."

I believe that the 2600 has a diameter of 28.3mm. 

1. I didn't think you did 'compromise' when it came to image quality?  Or is this all part of the experiment?

2. In the same sprit, would you plan to push on up to 32mm?

Anyway, good luck with this departure from the norm.  Who would have thought it?

Tony

[ollypenrice]

4 hours ago, AKB said:

I do note that the documentation for the RASA 8" says "~22mm diagonal is optimal", but I suppose that you simply had to test their statement  "...can also be used with larger sensors up to 32mm diagonal, ... though some compromise must be expected at the image periphery."

I believe that the 2600 has a diameter of 28.3mm. 

1. I didn't think you did 'compromise' when it came to image quality?  Or is this all part of the experiment?

2. In the same sprit, would you plan to push on up to 32mm?

Anyway, good luck with this departure from the norm.  Who would have thought it?

Tony

I went for this setup because Goran has demonstrated that it can work. I don't think there's much compromise being tolerated once the rig has been persuaded to work. Our setup is not yet working as well as his but we now feel happy with it, but we won't be trying a bigger chip in these optics.

It's true that I'm fussy about image quality but I'm not, and never have been, a pixel peeper. That's not my notion of a good image. My idea of a good image is one which has something to say and, ideally, something new. I don't like noise and nor do I like noise reduction so the RASA-CMOS combination ticks those boxes. Today I was processing 35 x 3 mins from this rig and, after a hard stretch, it looks slightly noise reduced when it's had none at all, which is quite impressive. Another plus is the sheer depth that the large aperture makes possible. And then there's the different 'look' that fast optics and OSC CMOS gives. It's a change, which is stimulating.

I think the biggest down side so far is that bright stars are themselves tight but they have an extended outer glow which is unlike refractor stars.

Above all, perhaps, this new rig has brought a fresh spark of excitement into my game.

Olly

[wimvb]

36 minutes ago, ollypenrice said:

I think the biggest down side so far is that bright stars are themselves tight but they have an extended outer glow which is unlike refractor stars.

That’s part of reflector territory. Imo, you have to either accept it or you fight it. I’ve accepted it. At least there are no spikes to worry about.

[Catanonia]

22 hours ago, ollypenrice said:

I can see the simplicity of sticking to a smaller chip size but, for me, 400mm isn't a focal length I'd instinctively use in search of high resolution. We're at 1.9"PP which won't be very seeing dependent and makes the system a good compromise between speed  (flux per pixel) and resolution. On the other hand the RASA should have the aperture to deliver higher resolution, certainly, when you have the seeing. Your sampling rate of 1.24 is, in principle, a viable galaxy imaging resolution. I'll be more than a little interested to see what you get on small, high res targets. The idea of just swapping the camera to go from widefield to high res has to be appealing!

Olly

I will certainly try it for example on M33 Triangulum and the bubble nebula and post the results when they come into view.

[ollypenrice]

9 hours ago, wimvb said:

That’s part of reflector territory. Imo, you have to either accept it or you fight it. I’ve accepted it. At least there are no spikes to worry about.

I agree. And the field illumination of the RASA 8 on an APSc chip is much flatter than that of my Tak 106 on a full frame chip. The Tak has a 23% light fall-off in the corners, making flats essential. I haven't done RASA flats yet but I've processed several images from it and haven't noticed any vignetting. It will be there but it can't be anything like 23%. And what about dust bunnies? I see none at all, but could this arise from the F ratio? The more out of focus the source of the bunny, the larger and softer will be its shadow, the bunny. In a steep F2 light cone the dust particles are going to be massively out of focus if I've got this right.

Olly

[tomato]

On the subject of diffraction artefacts created by the cables, has any body tried using flat profile cable and putting these edge on at 90 degrees to each other to create a faint 4 spike pattern?
 

I know flat usb cables have a poor quality reputation but I might give this a go when I put the RASA back on the mount.

[wimvb]

1 hour ago, ollypenrice said:

And what about dust bunnies? I see none at all, but could this arise from the F ratio? The more out of focus the source of the bunny, the larger and softer will be its shadow, the bunny. In a steep F2 light cone the dust particles are going to be massively out of focus if I've got this right.

Very likely so. Unless you go extremely deep in L, you may never see dust bunnies. A RASA is most likely combined with an osc camera, so you won’t get in a situation where you collect L only. Unless you go for a quad scope rig with permanently mounted LRGB filters.

I know that Göran keeps his gear so tidy that he never(?) uses flats. The little vignetting that he has can be dealt with in postprocessing.

Edited September 3, 2021 by wimvb

[wimvb]

35 minutes ago, tomato said:

On the subject of diffraction artefacts created by the cables, has any body tried using flat profile cable and putting these edge on at 90 degrees to each other to create a faint 4 spike pattern?
 

I know flat usb cables have a poor quality reputation but I might give this a go when I put the RASA back on the mount.

I think you will find it difficult to keep the cables perfectly straight, and you may end up with Drechsler’s solution.

[tomato]

5 hours ago, wimvb said:

I think you will find it difficult to keep the cables perfectly straight, and you may end up with Drechsler’s solution.

True, but you wouldn't need something as beefy as a full spider to keep the cables straight, (ultra thin CF strips would do it) and you would only need two of them. 

Some of the cables available are only 1.2 mm thick. I'll give this a try when I set up the RASA again, which will most likely be 2023 based on the last 8 weeks...

[gorann]

15 hours ago, ollypenrice said:

I agree. And the field illumination of the RASA 8 on an APSc chip is much flatter than that of my Tak 106 on a full frame chip. The Tak has a 23% light fall-off in the corners, making flats essential. I haven't done RASA flats yet but I've processed several images from it and haven't noticed any vignetting. It will be there but it can't be anything like 23%. And what about dust bunnies? I see none at all, but could this arise from the F ratio? The more out of focus the source of the bunny, the larger and softer will be its shadow, the bunny. In a steep F2 light cone the dust particles are going to be massively out of focus if I've got this right.

Olly

Yes, as @wimvb says I have not so far seen any reason to use flats, since as you also found Olly, there are no visible dustbunnies and a very even field illumination. A dose of Gradient Exterminator is all it takes. I also do not use darks with the ASI2600 as I cannot see any notisible effect of them. So for me it is Debayer -> Star alignment -> Image integration.

By the way I just got the first image from the double rig last night. However, when I checked it this morning one computer had stopped and logged out so I only got three frames from one of the RASAs. Still, the advantage of a double rig was that I at least got data from the other one. So here is this seasons first light. about 3 hours on LBN603:

Cheers, Göran

 

 

 

 

Edited September 3, 2021 by gorann

[GalaxyGael]

17 hours ago, ollypenrice said:

And then there's the different 'look' that fast optics and OSC CMOS gives. It's a change, which is stimulating.

Above all, perhaps, this new rig has brought a fresh spark of excitement into my game.

 

This is one exciting thing about fast optics, that I am also learning about. Even nebula imaging without any filter (duo, tri quad etc.), give lovely natural colours in stars obviously, but in reds/magentas/pinks and their relative intensities across frame, among other colors. 

With the 2600 MC, noise reduction is barely needed sometimes, especially in your  nearly-22SQM skies, you can also go very deep with reasonable resolution in a wide field. I never like star reduction of any degree, yet f/2.8 imaging gives a sparkle in filterless imaging, even from 20.02 SQM where I am on a good night.

On dust bunnies, I had never thought of that and assumed that me recent use of a feather blower that I got rid of all major dust, but maybe it is less sensitive to it - that's a bonus if true.

[GalaxyGael]

7 minutes ago, gorann said:

Yes, as @wimvb says I have not so far seen any reason to use flats, since as you also found Olly, there are no visible dustbunnies and a very even field illumination. A dose of Gradient Exterminator is all it takes. I also do not use darks with the ASI2600 as I cannot see any notisible effect of them. So for me it is Debayer -> Star alignment -> Image integration.

By the way I just got the first image from the double rig last night. However, when I checked it this morning one computer had stopped and logged out so I only got three frames from one of the RASAs. Still, the advantage of a double rig was that I at least got data from the other one. So here is this seasons first light. about 3 hours on LBN603:

Cheers, Göran

Ditto on the minimal (if ever) use of calibration frame with the 2600 MC. I did with my f/6 Maksutov-Newtonian, but it has the tiniest chip on the corrector and maybe a dust bunny was more obvious. Darks, bias etc. are never used (or at least I coudl not see a difference at full picture level, with or without). My f/2.8 scope I got recently, has mild vignetting, more so that these RASAs, but APP light pollution deals with it perfectly every time. So with fast data acquisition times, these scopes and this camera make things a litle easier with out absolute need for calibration frames.

A large solid state HDD on a decent PC makes real-time imaging and especially lucky imaging for DSOs much more accessible, with PI or Sharpcap live stacking options too.