20 replies to this topic

[vehnae]

Hello all, greetings from Finland!

 

This is my first image post to CN. During the summer break I acquired the Celestron RASA scope and since I haven’t seen too many pictures taken with this scope I figured I’d share. The setup that I use is the RASA fitted with a QSI690wsg camera riding on a 10Micron GM1000HPS mount. This combination gives me the image scale of 1.23”/px and a FWHM median of around 2.8” (15-second L exposure measured with PixInsight). I think that is scope-limited due to the short 620mm focal length. The 5-position QSI camera doesn’t quite fit inside the central obstruction so I use a small rectangular aperture mask over the camera to get cleaner diffraction spikes instead of covering much more aperture with a round mask. Also the wires from the camera are routed over the aperture using a 3D-printed round channel.

 

My jury is still out on using the RASA unguided, I have been getting a bit mixed results. The best models I have been able to obtain are a bit under 20” RMS (mirror locked during modeling), but the models have not been very comprehensive so far since our RoR is still under construction. If I’m not able to get consistent results unguided the backup option is to use a ASI120MM in the QSI’s OAG port that will then eliminate all mirror issues.

 

But on to the images! 

 

NGC 7000, LRGB 1h 40min, 5-minute unguided subexposures

 

LDN 673, LRGB 4h 5min, 5-minute both guided/unguided subexposures

 

VdB 152, LRGB 2h 45min, 5-minute guided subexposures

 

Melotte 15, SHO 7h 30min, 10-minute unguided subexposures

 

Thanks for looking, comments are welcome.

 

  ++ Jari

Edited by vehnae, 11 October 2015 - 04:04 AM.

[Raginar]

Nice job Jari, you should post in the beginner forum.  There is a bit more action in there... the CCD forum is a little dead.

[jhayes_tucson]

Those are fantastic images!  Very nicely done and thanks for sharing.

 

You must have super dark skies to be able to do 600s subs at F/2.2!  I suppose that the narrowband filters help a lot with that.  I use an OSC camera with my C14 at F/1.9 with a HyperStar adapter and I can't' ever get more than about 200s before the sky fog overwhelms things--even with our darkest skies (21.4 m/sq").

 

John

[dr.who]

Kari, those are some amazing images!

[Peter in Reno]

These are the nicest images I have seen taken with RASA!!!! I would continue whatever you are doing including unguided imaging. I see nothing wrong with the stars in ALL of your images.

 

Peter

[gezak22]

Very nice. There is a lot to like about the RASA. How sensitive is the tube/focuser to temperature variations?

[schmeah]

Excellent! I've been waiting to see some images with that scope. Fast, fast, fast!

 

Derek

[akulapanam]

Awesome shots!  If you don't mind me asking what adapter do you use to fit the QSI camera to the scope?  Also you should consider using a 50mm finder as a guider.  It will work fine up to about 1500mm which is a lot longer then the focal length of this scope.

Edited by akulapanam, 11 October 2015 - 11:06 PM.

[Goofi]

I'll just +1 to all the other praise shared ... really nicely done!

[DuaneS]

Sweet! I just bought an RASA and it will be here today hopefully. I do not have a CCD camera for it yet, still trying to decide on the best match. Keep us updated on your progress. Any recommendations would be great. Again, nice images!!

 

Duane

[bilgebay]

Very nice! Thanks for sharing! Can you share the picture of the cable channel please ? Also, an elliptical mask can help with the spikes better than a rectangular one I believe.

[josh smith]

Some really nice images there!  Always wondered how my 690 would look with RASA or Hyperstar.  Those are some high quality results, especially with lower integration time.

[akulapanam]

Very nice! Thanks for sharing! Can you share the picture of the cable channel please ? Also, an elliptical mask can help with the spikes better than a rectangular one I believe.

 

 

If you don't want spikes follow the instructions on this site.  Personally though I would really worry about them that much.

 

http://www.werbeagen..._hyperstar.html

[akulapanam]

Sweet! I just bought an RASA and it will be here today hopefully. I do not have a CCD camera for it yet, still trying to decide on the best match. Keep us updated on your progress. Any recommendations would be great. Again, nice images!!

 

Duane

 

The perfect camera for the RASA IMHO is the QSI6120 or ATIK 4120 because that chip will give the same FOV but with a 1" resolution.  Alternatively go really widefield with an Atik 11000.

[famax]

very nice results !

as for unguided imaging, it will requires at least less than 8" or 6" rms in your model results for long subs (>15 mn...).

flexure is your ennemy at most.perfect balance required, and careful refraction parameters and time management as well.

You can take advice on the 10 micron forum.

[james7ca]

These are all nice, but the colors in the shot of Melotte 15 are particularly impressive.

[vehnae]

Thank you for the kind words!

 

You must have super dark skies to be able to do 600s subs at F/2.2!

 

Not really, with a narrow (3-5nm) filter it's almost impossible to over-expose. The QSI camera has very low noise characteristics but still SGP estimates that the ideal exposure time for my f/2.2 setup would be around 8 minutes with a 5nm Ha filter. 

 

Very nice. There is a lot to like about the RASA. How sensitive is the tube/focuser to temperature variations?

 

I haven't yet lost frames due to temperature changes. That said, here the temperature is usually quite stable during the night. And my SGP is set to refocus in any case every hour or so.

 

If you don't mind me asking what adapter do you use to fit the QSI camera to the scope?

 

It's easy. RASA comes with a T2 adapter so I just have a suitable extension to fit the 690wsg with Astrodon filters. Actually I'm about 1mm too far compared to the nominal backfocus, it seems to result in slightly tighter stars.

 

Sweet! I just bought an RASA and it will be here today hopefully. I do not have a CCD camera for it yet, still trying to decide on the best match. Keep us updated on your progress. Any recommendations would be great. Again, nice images!!

 

In my opinion the big decision is whether to go OSC or mono, and if you go mono, are you content with filter drawers or do you require a filter wheel. Personally I chose the QSI camera because of the small footprint and integrated filter wheel. I can live with changing the wheel occasionally to image in LRGB or SHO, but I want the system to be able to handle one night independently. Also, the huge image circle just screams big cameras and deep images of large dark nebulaes. But that will rule out the use of any filter wheels. In any case your budget will decide the available options.

 

Very nice! Thanks for sharing! Can you share the picture of the cable channel please ? Also, an elliptical mask can help with the spikes better than a rectangular one I believe.

 

Here's a picture of the mask and channel. My friend didn't have black plastic for his 3D printer so I spray painted the other side black.

 

 

And here is the channel in business inside the scope, I taped some magnets to the side of the tube for attaching the channel. You can also see the size of the QSI camera in relation to the central obstruction.

 

 

And about diffraction spikes, since the QSI camera is not completely covered by the central obstruction it will create quite interesting stars. Here's an example with the channel only:

 

 

I don't mind the spikes, but the asymmetric look is a bit disturbing which is why I started using an aperture mask. With my mask the resulting spikes are much more symmetric:

 

 

  ++ Jari

Edited by vehnae, 14 October 2015 - 10:47 PM.

[akulapanam]

It looks like you are using the OAG...  I'm not sure if I would do that as it is easy to use a 50mm guide scope at that focal length/resolution.  That would help with the star issue.

[space_eagle28]

Very nice and crisp images

This scope is a winner.

[DuaneS]

 

Sweet! I just bought an RASA and it will be here today hopefully. I do not have a CCD camera for it yet, still trying to decide on the best match. Keep us updated on your progress. Any recommendations would be great. Again, nice images!!

 

Duane

 

The perfect camera for the RASA IMHO is the QSI6120 or ATIK 4120 because that chip will give the same FOV but with a 1" resolution.  Alternatively go really widefield with an Atik 11000.

 

Thanks for the info! I would like the 11000 chip for this scope. Would give great wide fields

 

Duane

[DuaneS]

Are there filter drawers available to use a monochrome camera with the RASA? I know that Starizona sells a unit for their Hyperstar. Not sure if it would work on the RASA. I would really like to go mono (but I am looking at the Atik 4120 too)

 

Duane