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Tight stars: RASA or Hyperstar?

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#1 dvb

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Posted 07 April 2020 - 03:54 PM

I've read that the images from RASA 8 and Hyperstar 8 are quite similar, but the RASA has "tighter" stars, while the Hyperstar can be a bit blobby. 

 

Can people share their experience of this?  Is the difference big enough to make the RASA a clear preference?

 

 

 



#2 DuncanM

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Posted 07 April 2020 - 04:33 PM

I've read that the images from RASA 8 and Hyperstar 8 are quite similar, but the RASA has "tighter" stars, while the Hyperstar can be a bit blobby. 

 

Can people share their experience of this?  Is the difference big enough to make the RASA a clear preference?

Theoretically, the RASA has tighter stars and a flatter, wider, corrected field. 

 

Practically, field size is limited by your camera and resolution is limited by camera pixel size, atmospherics and guiding.

 

Bottom line, IMHO, is that someone with Hyperstar who zealously optimizes every stage of the image acquisition process will probably get better images than a RASA owner, who's more casual about things, but if the RASA owner is equally zealous he/she will do better.


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#3 descott12

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Posted 07 April 2020 - 04:35 PM

I don't know about the stars but the HS gives you flexibility to use an existing SCT for visual and imaging, and at a range of focal lengths.  To me that is a big plus. I am reconfiguring mine all the time and I love being able to do so many things with it.

Of course, if you only care about imaging and/or you don't already own an SCT, then I would think the RASA is the way to go


Edited by descott12, 07 April 2020 - 04:36 PM.


#4 bobzeq25

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Posted 07 April 2020 - 04:42 PM

I've read that the images from RASA 8 and Hyperstar 8 are quite similar, but the RASA has "tighter" stars, while the Hyperstar can be a bit blobby. 

 

Can people share their experience of this?  Is the difference big enough to make the RASA a clear preference?

It all depends on whether you want the option of removing the Hyperstar.  At the short focal length, RASA is significantly better.  Everything has been optimized for that.  It matters.


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#5 dvb

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Posted 07 April 2020 - 07:27 PM

OK, I guess in fairness I should 'fess up: I do have an Edge HD800, but I did not want to bring that into the equation, because to me it doesn't matter: Yes, there would be practical and financial advantages to getting the Hyperstar 8 for it:  Just one scope to pack, cheaper . . . . But, it would not be cheaper for me if, having laid out the cash for the Hyperstar, I just had to shell out for the RASA anyway because I was dissatisfied with the Hyperstar images.  I am fortunate that I can afford to own both the HD800 and the RASA 8 if that is what it takes to get satisfying images.  

 

So, for me the only issue is which one will produce the "tighter stars".  

 

(Altho, now that I think of it, I have also heard the colours are better with the RASA.)



#6 andysea

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Posted 09 April 2020 - 12:18 AM

If that helps, I typically get a fwhm of around 3" with my RASA 8 and ZWO ASI1600 mm camera. I may have gotten better results than that on rare nights of perfect seeing.

I figured that for such a wide field that would be acceptable. The stars are very good to the corners. I don't now what is the performance with an APS-C sensor.


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#7 bobzeq25

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Posted 09 April 2020 - 05:19 PM

If that helps, I typically get a fwhm of around 3" with my RASA 8 and ZWO ASI1600 mm camera. I may have gotten better results than that on rare nights of perfect seeing.

I figured that for such a wide field that would be acceptable. The stars are very good to the corners. I don't now what is the performance with an APS-C sensor.

I get similar results on average nights.  On good nights I've done better (after tightening/adjusting the scope/camera connection with a PreciseParts adapter, which took a while to figure out).  Here's better.  The FWHM is pixels, multiply by 1.2 for arc sec.  Click on the picture to enlarge, the center picture is a mosaic of the center and edges.  I'd be surprised if someone could get corner stars that looked like that with Hyperstar.

 

Heads up, tilt is a big issue with the scope (F2 is extremely sensitive to tilt).  Different people have found different solutions. 

 

RASA OSC sample.jpg


Edited by bobzeq25, 09 April 2020 - 05:32 PM.

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#8 dvb

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Posted 14 April 2020 - 09:48 AM

Thanks to all for your replies. Sounds like the RASA is slightly better, but not massively, so I’ll go with the Hyperstar.


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