6 replies to this topic

[bec]

Hello All

8” ROWE-ACKERMANN SCHMIDT ASTROGRAPH (RASA 8)

 

I am thinking of ordering one of these scopes.  Or am I basically downsizing.   Any pros/cons appreciated.

 

I have the following setup

9.25 Edge HD

CEM60

Hyperstar

ASI296 mc pro

T5i dslr

asiair pro

I did a quick search and didn't find any link to this scope on CN

 

Any thoughts appreciated.  I decided to keep my cem60 and not order the cem70g so can look at other things.

 

Thanks

bec

Edited by bec, 26 November 2020 - 12:23 AM.

[string]

I would not see the RASA8 as a downgrade. It's possibly the best deal for F2 imaging on the market. The FOV would be better than the EdgeHD/hyperstar 9.25. You can see the difference in FOV for yourself on astronomy.tools on the web.  Just enter your EDGEHD9.25/Hyperstar specs and the RASA8 and see exactly the strengths of both on a variety of targets. Cool site! You would loose the ability to take off the hyperstar if you want to do visual. However, the hyperstar setup you are running makes for a heavier (top heavy) rig if all you want to do is F2 imaging. The RASA wins on sheer convenience and you can even do twin RASA8s like Steven Morris:

 

https://www.youtube....WsIdm6pU&t=343s

 

There's a great facebook group dedicated to RASA imaging:

 

https://www.facebook...341262949302876

 

I'd love to see a RASA8 discussion start right here.

 

Check my Signature... I lost my RASA 11.  I also own a 9.25 (no hyperstar yet)... I'm going with a RASA8... if not TWO!

Edited by string, 26 November 2020 - 02:51 AM.

[carolinaskies]

RASA 8 major hilites
pros
F/2 widefield short imaging time
guiding not critical, very widefield imaging

cons 
limited to non-dslr cameras(some mirrorless but mainly up to APS-C dedicated CMOS)
optical window & filter use can be tricky and require extra expense especially for 'fast' filters 




 

[string]

RASA 8 major hilites
pros
F/2 widefield short imaging time
guiding not critical, very widefield imaging

cons 
limited to non-dslr cameras(some mirrorless but mainly up to APS-C dedicated CMOS)
optical window & filter use can be tricky and require extra expense especially for 'fast' filters 




 

I have a question about what you said about fast filters. My backyard is Bortle 6. One of my Favorite filters to date on non-rasa instruments is the Optolong L eXtreme. Would that be a filter I could continue using on a RASA or would I be better off with another narrow band filter or the Celestron light pollution filter maybe?

[carolinaskies]

I have a question about what you said about fast filters. My backyard is Bortle 6. One of my Favorite filters to date on non-rasa instruments is the Optolong L eXtreme. Would that be a filter I could continue using on a RASA or would I be better off with another narrow band filter or the Celestron light pollution filter maybe?

I should have said, narrowband filters need to be fast-filters, normal RGB filters are OK to use.

You can try the L-eXtreme out since you already have it, worst effect is losing a bit of aperture due to the light cone cutting off the pass. 

The reasoning behind the F/2 hi-speed filters for narrowbands H-alpha, OIII, S-II is the band-pass is increased to (10-12nm) which allows enough light to pass at the high speed vs the standard 8nm for narrow band which will clip the light. 

  
 

[decep]

I have a question about what you said about fast filters. My backyard is Bortle 6. One of my Favorite filters to date on non-rasa instruments is the Optolong L eXtreme. Would that be a filter I could continue using on a RASA or would I be better off with another narrow band filter or the Celestron light pollution filter maybe?

There is a graph floating around that shows the passthrough of the l-extreme, l-enhance, and l-pro at different focal ratios.

 

The l-extreme (and any 7nm filter) is pretty harsh to a f/2 light cone.  I believe the passthrough was <40%.  The l-enhance with its 12nm bandwidth fared better, especially for h-alpha.

 

Found it:  http://karmalimbo.co...ter_Aug2020.pdf

 

I have imaged with the l-extreme with Hyperstar... during a full moon no less.  I did not notice any major issues

[string]

I should have said, narrowband filters need to be fast-filters, normal RGB filters are OK to use.

You can try the L-eXtreme out since you already have it, worst effect is losing a bit of aperture due to the light cone cutting off the pass. 

The reasoning behind the F/2 hi-speed filters for narrowbands H-alpha, OIII, S-II is the band-pass is increased to (10-12nm) which allows enough light to pass at the high speed vs the standard 8nm for narrow band which will clip the light. 

  
 

I just ordered two of  the IDAS NBX-RS. The RS is the second gen NBX that will be out in early January. They are rated for use on f/2 systems with the associated band shift.