A few hours on M31 with the RASA8

[Catanonia]

I am currently running my 30 panel SADR mosaic, but after about 10:30pm, it gets too close to the horizon for my liking and I am normally hunting for a target to make the best use of the rest of the night

Our closest galactic neighbour, M31 is up high, so I swung the RASA 8 across and set it to capture 2min exposures. 

I managed to get in about 60 of them, so 2 hours worth and this morning got the processing done. 

I "tried" to keep natural colours  and not all those "purple" images you see of M31. Hopefully I did it proud as the colours look correct, especially when you look at the star colours.

 

Equipment

• RASA8 telescope and EQ8-R mount
• ZWO 2600MC Pro main camera with ASI 120mm guide
• ASIAir 
• Processed in PixInsight

[Alien 13]

I like it very much, so natural.

Alan

[old_eyes]

Damn these RASAs are good. Great image!

[Adreneline]

18 hours ago, Catanonia said:

I "tried" to keep natural colours  and not all those "purple" images you see of M31.

This is always a difficult call - what is natural and what is not natural. My personal preference is no hint of magenta in an image but that is purely a personal thing - I know lots of folk like to see magenta (or hints of) and I know some really like the Hubble'esque look on narrowband images.

Hope you don't mind but based on your comment above I took a look at the image in PI and in particular the histogram:

I then applied iSCNR and looked again:

I guess the question is "which is more natural"?

Does an aligned histogram imply more "normal" - whatever normal might be. It's a tough one.

All down to personal preference I would suggest.

[gorann]

Really nice! Time is apparently never too short for a RASA😉.

I am a bit puzzled by the halo around the bright blue star. Looks like en internal reflection in a filter, but do you use a filter? I shoot without any filter when I do RGB with the RASA and ASI2600MC. Also those asymmetrical flares from brighter stars are a bit odd. How do you arrange the camera cables? Hopefully you do not have the same issues as Alan describes in this thread:

CS, Göran

 

[wimvb]

1 hour ago, gorann said:

How do you arrange the camera cables?

I think you can see the shadow of the semicircle that holds the cables in the halo of the bright star. Looks very much like your solution, Göran.

very nice image @Catanonia

[Adam J]

3 hours ago, gorann said:

Really nice! Time is apparently never too short for a RASA😉.

I am a bit puzzled by the halo around the bright blue star. Looks like en internal reflection in a filter, but do you use a filter? I shoot without any filter when I do RGB with the RASA and ASI2600MC. Also those asymmetrical flares from brighter stars are a bit odd. How do you arrange the camera cables? Hopefully you do not have the same issues as Alan describes in this thread:

CS, Göran

 

I agree that halo is not normal and I think that something is wrong with the scope. Lots of people with similar issues recently. OP I would contact your supplier. 

Adam 

Edited November 15, 2022 by Adam J

[ollypenrice]

1 hour ago, wimvb said:

I think you can see the shadow of the semicircle that holds the cables in the halo of the bright star. Looks very much like your solution, Göran.

very nice image @Catanonia

We find no artifacts with this arrangement...

You do have an issue somewhere along the line, though, as shown by the blue stars. They show fantail-like flares radiating out from the centre. This may come from your cable arrangement but there was an SGL thread fairly recently about this. It seems a large batch of RASAs came from China with a defect producing this effect. Celestron are looking into it.

Your colour looks fine to me, as does most of the image. I'd be wanting to soften the transition in brighteness atthe core, though.

Olly

Edit! crossed posts with Adam, there, who beat me to it.

Edited November 15, 2022 by ollypenrice
Clarification

[Adam J]

4 minutes ago, ollypenrice said:

 

You do have an issue somewhere along the line, though, as shown by the blue stars. They show fantail-like flares radiating out from the centre. This may come from your cable arrangement but there was an SGL thread fairly recently about this. It seems a large batch of RASAs came from China with a defect producing this effect. Celestron are looking into it.

 

Olly

I don't think its cables Olly as the fan tail is moving to a different rotation in different parts of the image always pointing outwards from the centre of the optical axis. So its more likely a optical problem, probably with the edge of the primary mirror. 

Edited November 15, 2022 by Adam J

[wimvb]

50 minutes ago, ollypenrice said:

We find no artifacts with this arrangement

Agreed, both Göran and you use a similar cable management with good result. I just commented on Göran's question. Your and Adam's suggestion that this might be the scope itself is very plausible. The OP also has a slight tilt issue, because stars in the right hand side corners are elongated and radiating outward.

[ollypenrice]

2 hours ago, Adam J said:

I don't think its cables Olly as the fan tail is moving to a different rotation in different parts of the image always pointing outwards from the centre of the optical axis. So its more likely a optical problem, probably with the edge of the primary mirror. 

Agreed.

Olly

[symmetal]

5 hours ago, gorann said:

Hopefully you do not have the same issues as Alan describes in this thread:

I'm afraid it's the same issue Göran though is being masked somewhat by the odd blue halos. If you contact Celestron they will fix it but it needs sending back to China for a replacement mirror and at the time, (a month ago), Celestron didn't know how long this process would take, as they've also returned all their RASA 8 stock to China because of this issue.

Under guarantee they will hopefully just replace the scope with a new one, once the issue has been resolved and they have fresh stock but it's worth contacting your supplier to make them aware of this issue.

In the meantime you can make an aperture mask of around 180mm diameter which will solve the asymmetrical flaring issue over the majority of the image though it then becomes an f2.2 scope rather than f2.

Alan

[tomato]

2 hours ago, ollypenrice said:

We find no artifacts with this arrangement...

You do have an issue somewhere along the line, though, as shown by the blue stars. They show fantail-like flares radiating out from the centre. This may come from your cable arrangement but there was an SGL thread fairly recently about this. It seems a large batch of RASAs came from China with a defect producing this effect. Celestron are looking into it.

Your colour looks fine to me, as does most of the image. I'd be wanting to soften the transition in brighteness atthe core, though.

Olly

Edit! crossed posts with Adam, there, who beat me to it.

I thought the cable circle should all lie within the scope aperture?

[Tomatobro]

3 minutes ago, tomato said:

I thought the cable circle should all lie within the scope aperture?

So did I. If not then would it not be like a Newtonian secondary spider?

[ollypenrice]

7 minutes ago, tomato said:

I thought the cable circle should all lie within the scope aperture?

That didn't work for us. It gave slanted outer halos rather wittily parodied by vlaiv!  Maybe I did something wrong but, with our system as illustrated, we get pretty good stars across the chip - even if they are not Takahashi/TEC 'good.' But, hey, for refractor stars the trick is to use a refractor!!! 🤣

If it works for you, stick with it.

Olly

[ollypenrice]

7 minutes ago, Tomatobro said:

So did I. If not then would it not be like a Newtonian secondary spider?

Depends what kind of spider. Some Newts, including Obsession and David Lukehurst, use a spider shaped as our cables are shaped. The net degree of artifact is the same as a cross-vaned spider but it is spread around the entire circle. (I have this on the reliable authority of optical genius Ralf Ottow.) It is possible to use a RASA with a cross-vaned cable equivalent but, personally, I really don't like star spikes.

Olly

[Catanonia]

I am using a LP filter that I think is giving the halo. I also have the cables routed by a semi circle cable router similar to Olly’s  that gives that artefact on the bright stars

Edited November 15, 2022 by Catanonia

[gorann]

1 hour ago, Catanonia said:

I am using a LP filter that I think is giving the halo. I also have the cables routed by a semi circle cable router similar to Olly’s  that gives that artefact on the bright stars

As you see from the comments here, the flares around your stars should not be there and are most likely a result of a defect in the primary mirror that appears to have affected a big batch of RASA8 that Celestron has sent out, but promised to fix (as I understand it). So you should really contact your dealer and ask for a replacement. Sorry for the bad news, but a proper RASA8s (like mine) will not produce such stars.

[wimvb]

4 hours ago, tomato said:

I thought the cable circle should all lie within the scope aperture?

 

4 hours ago, Tomatobro said:

So did I. If not then would it not be like a Newtonian secondary spider?

 

4 hours ago, ollypenrice said:

That didn't work for us. It gave slanted outer halos rather wittily parodied by vlaiv!  Maybe I did something wrong but, with our system as illustrated, we get pretty good stars across the chip - even if they are not Takahashi/TEC 'good.' But, hey, for refractor stars the trick is to use a refractor!!! 🤣

If it works for you, stick with it.

Olly

 

4 hours ago, ollypenrice said:

Depends what kind of spider. Some Newts, including Obsession and David Lukehurst, use a spider shaped as our cables are shaped. The net degree of artifact is the same as a cross-vaned spider but it is spread around the entire circle. (I have this on the reliable authority of optical genius Ralf Ottow.) It is possible to use a RASA with a cross-vaned cable equivalent but, personally, I really don't like star spikes.

Olly

You all may find this old thread interesting. From across the pond

 

https://www.cloudynights.com/topic/495707-spider-and-secondary-diffraction-what-to-do-what-to-avoid/

[Catanonia]

12 hours ago, gorann said:

As you see from the comments here, the flares around your stars should not be there and are most likely a result of a defect in the primary mirror that appears to have affected a big batch of RASA8 that Celestron has sent out, but promised to fix (as I understand it). So you should really contact your dealer and ask for a replacement. Sorry for the bad news, but a proper RASA8s (like mine) will not produce such stars.

Gorann,

Attached is  a couple of single subs, 1 minute (2xbin) and 2 minute (1xbin)

[gorann]

Yes, those star flares appear to be quite characteristic for the problem with the mirror of a batch of RASA8. @symmetal had his RASA8 replaced three times (see the link I gave) before he gave up and bought a RASA11. But, if it does not bother you then it may not be a problem and you can enjoy a very fast and capable telescope. But as I understand it from @symmetal thread Celestron is working to solve the problem and maybe you can get it replaced at some point if you contact your dealer. The problem is more clearly described in this thread:

 

Edited November 16, 2022 by gorann

[Catanonia]

4 minutes ago, gorann said:

Yes, those star flares appear to be quite characteristic for the problem with the mirror of a batch of RASA8. @symmetal had his RASA8 replaced three times (see the link I gave) before he gave up and bought a RASA11. But, if it does not bother you then it may not be a problem and you can enjoy a very fast and capable telescope. But as I understand it from @symmetal thread Celestron is working to solve the problem and maybe you can get it replaced at some point if you contact your dealer. The problem is more clearly described in this thread:

 

mmm, going through some old images with the rasa8 and it can be clearly seen here on the HorseHead

[gorann]

When did you buy it and where? Most dealers would help you, like FLO tried to help @symmetal

[Catanonia]

2 hours ago, gorann said:

When did you buy it and where? Most dealers would help you, like FLO tried to help @symmetal

Just over a year ago from Astronomy365

I will contact Zoltan and find out options

Edited November 16, 2022 by Catanonia