First light with RASA8, ASI2600, and new obsy

[gorann]

I have been at the lookout for a wide field scope (what some people call astrographs) and this spring I came across a nearly unused RASA8, and after 6 months waiting time, due to the virus situation, I finally received an ASI2600MC - an APS-C sized cooled OSC with relatively small pixels (3.76 µm) that kind of fit the 400 mm FL of the RASA8 (ca 2 "/pix sampling). As I allready had my two obsies filled up with other scopes I decided to spend the summer building a third obsy for the RASA to put on my long-time retired NEQ6, my first mount bought in 2014 when I started my AP adventure, but having been laying in a closet for the last five years, beeing replaced by an EQ8 and a Mesu in my other obsies.

Up here astrodarkness started a few days ago, and on Saturday I could finally get the first light out of the RASA and ASI2600. I thought I would go for something simple, at least something I could easily find with the NEQ6 and hand controller: M31.

I have to say I am very impressed with both the scope and camera. The collimation of the RASA was spot on (round defocused stars) and it maintained focus all night, although all night here is now only three hours. I am equally impressed with this new ASI camera. As promised there is no amp glow so no need for darks. There was also virually no vignetting by the RASA8 although it is stated to perform best up to an image circle of 22mm. The diagonal of the ASI2600 is 28mm. However, the stars in the corners were a bit elongated, probaly due to minor tilt, but trying to fix that on an f/2 telescope could be quite challenging and it will at least not be my first priority. Andromeda fitted with margin so I could crop away the edges.

I don't think anything I have set up to do in AP has been as smooth as this. Fortunately I found that Baader make a 7.5 mm T2 extension that is what is exactly needed to fit the ASI2600 to the T2 adapter of the RASA to get to the 29 mm chip distance. The ASICAP program I use for my older ASI cameras did not work with the 2600 but I soon found out that there is a new ASICAP hidden within the new bundle called ASIStudio. Focus was easy and it kept all night - I have heard that about the RASA before (like on Chuck's Astrophotography on Youtube).

So my conclusion is that the RASA8, even being an f/2 scope, which is supposed to be extremely tricky to use, is very easy to get working. I think that bad rumour may come from the Hyperstar attachement that you can fit to SCT scopes, but the RASA is dedicated to this and apparently hardly ever needs collimation. Olly @ollypenrice, may have a comment?

My only complaint so far is the star shapes that may not impress pixel peepers (including me) but I think I can improve on them by organizing the two cables to the camera in a curved form - I am trying that out tonight on M33 (EDIT: It worked, se my M33 post).

So, enough rambling about the RASA, here are my first 90 minutes (180 x 30 seconds at gain 100) aquired with the RASA8 and ASI2600. No flats (I did take some but it looked better without) and no darks (not needed with the ASI2600). Stacked in PI and processed in PS. I also tried 70 x 60 seconds at gain 0, and it looked similar but not really as good.

I should make a thread about the obsy build - I had to go to plan C before it worked out.

Cheers

Göran

EDIT: at the bottom I added a non-cropped version including both the gain 0 and gain 100 data, so totally 160 minutes and a bit more dust and core details.

 

Edited August 19, 2020 by gorann

[Datalord]

The RASA really is a remarkable scope. Very well done! And congratulations!

[gorann]

9 minutes ago, Datalord said:

The RASA really is a remarkable scope. Very well done! And congratulations!

Thanks Datalord! Yes, it is remarkable, especially since it will not break the bank compared to all other "astrographs".

[tomato]

That's a stunning M31, you have got this combination working wonderfully right out of the box.

[gorann]

2 minutes ago, tomato said:

That's a stunning M31, you have got this combination working wonderfully right out of the box.

Thanks! Yes I am quite plesed and last night I also organized the camera cables better so I got rid of the spikes, as seen in my M33 image (just posted).

[tomato]

Yes, it's given me real food for thought. I need a 12 panel mosaic with the Esprit 150s and KAF 8300 cameras to get a similar FOV. That's at 1.06 arcsec/pixel, but would it show any more detail than your image?  More significantly, it will take me weeks to get the data, even with the dual rig.

 

[tooth_dr]

What a beautiful image Goran, that is a really ideal FOV for M31.  On a small note, there is some smudging on the left hand side of the image, just a registration error/stacking artefact?

[Laurin Dave]

Excellent Goran...   but a RASA and a OSC...  tut tut, what is the world coming too

Dave

[gorann]

23 minutes ago, Laurin Dave said:

Excellent Goran...   but a RASA and a OSC...  tut tut, what is the world coming too

Dave

Thanks! Yes, nothing is what it used to be. Olly just posted a OSC image on Astrobin.....

[gorann]

26 minutes ago, tooth_dr said:

What a beautiful image Goran, that is a really ideal FOV for M31.  On a small note, there is some smudging on the left hand side of the image, just a registration error/stacking artefact?

Thanks! I will check the smudge.

[gorann]

1 hour ago, tomato said:

Yes, it's given me real food for thought. I need a 12 panel mosaic with the Esprit 150s and KAF 8300 cameras to get a similar FOV. That's at 1.06 arcsec/pixel, but would it show any more detail than your image?  More significantly, it will take me weeks to get the data, even with the dual rig.

 

Ha ha! The RASA is imaging near 2 arcsecs/pix so you may beat it at nights with good seeing if you pixel peep. Why not do as I and get a RASA and give it its own obsy. My double Esprits are still in Obsy 1 on the Mesu waiting eagerly for the nights to get longer😃

[tomato]

Two observatories in my back garden would be a step too far for Mrs Tomato, but @Tomatobro is seriously considering a permanent observatory so there could be options.

Mind you, with a result like that obtained with 90 mins of data I would have time to set up and take down...

[Allinthehead]

Congratulations on your new setup and a great first light.

[gorann]

2 minutes ago, Allinthehead said:

Congratulations on your new setup and a great first light.

Thanks a lot Richard! I wonder how the RASA compares to Epsilons - it is certainly much cheaper on a price to aperture comparison.

[Allinthehead]

1 minute ago, gorann said:

Thanks a lot Richard! I wonder how the RASA compares to Epsilons - it is certainly much cheaper on a price to aperture comparison.

Faster too. 

[ollypenrice]

The image is very good but it doesn't include all of M31. If you went deeper you'd find distinct structure running out of your present frame on the left hand side. I guess I'd better prove that! 😁

However, with a scope like this I'm sure you could catch the lot and possibly go deeper than mine. The key thing is that it's giving you not just the speed but nice small, tight stars. Few Hypersatar broadband images do this. There are certainly some good Hyperstar narrowband images around. My real beef with Starizona is their mendacious advertising in which they talk about images with and without the Hyperstar as if they were in some way the same images. They are, of course, most certainly not the same images.

I think your scope-camera combination has done a great job and I'm very impressed.

Olly

[ollypenrice]

7 hours ago, gorann said:

Thanks! Yes, nothing is what it used to be. Olly just posted a OSC image on Astrobin.....

And on here...

I don't want to sidetrack this thread but I've posted lots of OSC images on here and elsewhere... It was on the basis of this experience that I developed a preference for mono. The modern CMOS cameras seem to be in a different league to the two OSC CCD cameras I've owned.

Olly

Edited August 18, 2020 by ollypenrice

[gorann]

Thanks a lot Olly! Yes, I think the RASA is quite different from the Hyperstar, and yes I remember your wide and deep M31 image but not many scope/camera combinations include all of M31. Was your image a mosaik? Maybe when it gets darker here I should do a 10 hour run in a night and see how deep I can get with the RASA. Should correspond to 120 hours at f/7 if I rapidly calculated it correctly.

[gorann]

15 minutes ago, ollypenrice said:

And on here...

I don't want to sidetrack this thread but I've posted lots of OSC images on here and elsewhere... It was on the basis of this experience that I developed a preference for mono. The modern CMOS cameras seem to be in a different league to the two OSC CCD cameras I've owned.

Olly

Yes, the ASI2600MC is amazing - virtually no noise (at least I have not felt any need for NR so far) and no amp glow whatsoever (no darks needed). My previous generation CMOS OSC (ASI071) is great but darks were needed and this one is one step up. The one problem is stacking time: each 26 Mpixel file is 50 Mb and with the RASA I get about one such file per minute.....

Edited August 18, 2020 by gorann

[ollypenrice]

1 hour ago, gorann said:

Thanks a lot Olly! Yes, I think the RASA is quite different from the Hyperstar, and yes I remember your wide and deep M31 image but not many scope/camera combinations include all of M31. Was your image a mosaik? Maybe when it gets darker here I should do a 10 hour run in a night and see how deep I can get with the RASA. Should correspond to 120 hours at f/7 if I rapidly calculated it correctly.

Yes, mine was a 2 panel with a full frame CCD at 530mm FL. I was intrigued by the size of M31 as shown on the sky charts because it was larger than any image I'd ever taken at that point. I'd also seen an image with the upturned outer glow on the left of our images. (I've never managed to find that image again.) I had lots of data in 15 minute subs but when I went to 30 minutes I got it.

I think these calculations are difficult. To my mind the key question is, 'How much area of aperture do you have per area of pixel?' (And then, of course, pixel sensitivity comes into it as well.)

Olly

[smr]

Fantastic image Goran, and a nice write-up. I am very tempted to buy the ASI2600. I've noticed that there seems to be quite a lot of ASI2600 owners with fast scopes though, in the f/2 or f/3 range of light gathering capability and I'm wondering if I would need to buy a RASA 8 as well to make full use of the Camera or whether it should work well with my f/5.9 Z73.

[ian_bird]

2 hours ago, ollypenrice said:

Yes, mine was a 2 panel with a full frame CCD at 530mm FL.

I remember us sitting down and planning that 2 panel mosaic in your cave! We hung the mosaic off of the blue star at the top.

You wanted M31 to be horizontal. I wanted a slight slope.

Luckily - I won! (In my opinion!)

Happy days!

Best Regards

Ian

 

[gorann]

6 hours ago, smr said:

Fantastic image Goran, and a nice write-up. I am very tempted to buy the ASI2600. I've noticed that there seems to be quite a lot of ASI2600 owners with fast scopes though, in the f/2 or f/3 range of light gathering capability and I'm wondering if I would need to buy a RASA 8 as well to make full use of the Camera or whether it should work well with my f/5.9 Z73.

Thanks! Your scope has about the same focal length as a RASA8 (ca 400 mm) so you would like a camera with small pixels to get a good resolution (arcsecs per pixel). With your scope the ASI2600 would give you 1.85 arcsec/pixel and I do not know if there is an APS-C sized camera with smaller pixels than this one. ASI071 has larger pixels so it would be worse (more undersampling). You can check it with Astronomy Tools on the net. The advantage with the RASA over your scope is that it is faster (collects more photons per unit of time because of the larger aperture) but many would say that f/5.9 is fast enough:

[gorann]

On 18/08/2020 at 22:58, ollypenrice said:

The image is very good but it doesn't include all of M31. If you went deeper you'd find distinct structure running out of your present frame on the left hand side. I guess I'd better prove that! 😁

However, with a scope like this I'm sure you could catch the lot and possibly go deeper than mine. The key thing is that it's giving you not just the speed but nice small, tight stars. Few Hypersatar broadband images do this. There are certainly some good Hyperstar narrowband images around. My real beef with Starizona is their mendacious advertising in which they talk about images with and without the Hyperstar as if they were in some way the same images. They are, of course, most certainly not the same images.

I think your scope-camera combination has done a great job and I'm very impressed.

Olly

To see how much dust I can get out of the data I have, I merged the 90 minutes of gain 100 data (used in the previous version) with the 70 minutes of gain 0 I collected the same night, so totally 160 min. I then also did not crop it. Now I think I have caught the full extension of the galaxy dust except a tiny bit at the very left edge. If I frame it carefully and have another go at M31 with the RASA I could get it all in, but then there are so many other interesting objects to aim at.....

Still quite happy with how deep I could go with less than 3 hours of data and I found a bit more details in the core.

 

Edited August 19, 2020 by gorann

[tomato]

Very impressive, I can feel another astro spend coming on...