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Celestron RASA 8" or Edge HD 8" with a HyperStar?

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#26 Tapio

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Posted 09 September 2018 - 02:06 PM

I believe Bahtinov masks for Hyperstar are two piece sets.
I also believe RASA scope requires equally careful collimation as Hyperstar.

#27 suvowner

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Posted 10 September 2018 - 12:16 PM

The 8" RASA is 24" long, whereas the 8" Edge is 17" long.  With a Schmidt corrector, the farther away from the primary mirror it is, the better corrected the FOV is (to a point).  The larger spacing between the corrector and mirror in the RASA probably leads to a better corrected FOV.

 

The larger spacing (or perhaps a re-worked corrector) likely leads to less spherochromatism, which may be why Celestron is emphasizing the wavelength range for the RASA.  A "standard" F/2+5x SCT is only well corrected at green wavelengths, and suffers from undercorrection in IR, and severe overcorrection in deep blue and violet wavelengths.  

total length is different, but with the c8 the corrective lens elements are on the front of the scope, the hyper star is about 6-7" long, so the distance from the mirror to the front corrective elements is pretty darn close between the 2.......

 

Dylan Odonnel has demonstrated the starizona hyper star filter slider works well on the rasa.......

 

this is quoted directly from Mark Ackermann on Dylans youtube video comments about the rasa:

Dylan, also, after reading some of the comments below, I should like to make this information available to your viewers.  The real difference between the RASA-11, and a C-11 with a Hyperstar, is that the RASA-11 was designed to give a wider field of view without any significant vignetting, and the RASA-11 is corrected for a wider range of colors than the Hyperstar.  The Hyperstar approach is good for those who want to do some occasional fast imaging, but the RASA-11 is a real monster in terms of being a true wide-field instrument with exceptional color correction.

 

 

​I think you could extrapolate this to the 8" rasa as well, the wider range of color correction might be helpful in some situations, but I would think only if imaging with a osc camera. 

 

however the rasa 11 image circle is 43mm, whereas the 8" is only 22mm......so not really much improvement in field of view over the hyper star at the 8 inch aperture 



#28 evan9162

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Posted 10 September 2018 - 02:52 PM

total length is different, but with the c8 the corrective lens elements are on the front of the scope, the hyper star is about 6-7" long, so the distance from the mirror to the front corrective elements is pretty darn close between the 2.......

 

 

That's not what I'm talking about.  The quality of correction of a Schmidt-corrected telescope varies depending on the separation between the Schmidt corrector and the primary mirror.  The spacing between the Schmidt corrector plate and primary mirror on commercial SCT's is actually sub-optimal (they are too close together to fully correct coma).  This is done to make the telescope a much more compact size.

 

In the RASA, they have placed the Schmidt corrector farther from the primary mirror, likely improving correction for coma and other off-axis aberrations.  In addition, wider spacing may be responsible for reduced spherochromatism, so the RASA has a wider range of wavelengths that it's well corrected for.


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#29 bobzeq25

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Posted 10 September 2018 - 05:31 PM

It seems clear that the Hyperstar scope is more versatile, the RASA is optimized to be better at the short focal length stuff.  How much?  Who knows?  Nobody, until there's some experience.



#30 rockstarbill

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Posted 10 September 2018 - 05:36 PM

Better color correction in the RASA. I'm not sure the RASA8 will be much different than its larger brothers. Well, other than the 8 and 14 having new focusers.

#31 lucutes

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Posted 10 September 2018 - 06:23 PM

I believe Bahtinov masks for Hyperstar are two piece sets.
I also believe RASA scope requires equally careful collimation as Hyperstar.

Where would one purchase a two piece Bahtinov Mask?


The 8" RASA Manual appears to be out.
https://celestron-si...5Lang_PROOF.pdf 



#32 einarin

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Posted 10 September 2018 - 11:56 PM

Didn't find ready made but not that difficult to cut one in half.

https://www.cloudyni...e-hyperstardlsr

http://mike-wiles.bl...hyperstar.html/



#33 suvowner

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Posted 11 September 2018 - 09:30 AM

Where would one purchase a two piece Bahtinov Mask?


The 8" RASA Manual appears to be out.
https://celestron-si...5Lang_PROOF.pdf

would be much better off getting a motorized focuser, the most affordable way to do it I know of is a jmi motofocus and shoestring astronomy fcusb focus controller 


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#34 Astrojedi

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Posted 14 September 2018 - 01:48 PM

I currently have a Celestron EdgeHD 8" scope and CGEM II mount, and recently been researching the HyperStar by Starizona as I want to do faster, wider-field, astrophotography.  For those not familiar, the HyperStar would turn my existing f/10 EdgeHD scope in to a faster f/2 imaging system.

 

However, I just saw the announcement today of Celestron's new 8" f/2 RASA: https://www.celestro...trograph-rasa-8.

 

So I'm wondering whether I should still go with the HyperStar for my EdgeHD scope (about $1,000), or wait and go for the more expensive Celestron 8" RASA ($1,699) that's due to be released in the coming months.

 

I have a ZWO ASI1600MM-Cool camera which I intend to continue using. Does anyone have experience with the Celestron RASA system, specifically in using monochrome cameras along with LRGB & narrowband filters?  Would that setup work?  Is there some kind of filter drawer system for the RASA?

 

And would the RASA in theory deliver significantly better images than a HyperStar and EdgeHD 8"?  Has anyone here had experience with both the HyperStar system and the existing larger Celestron RASA scopes?

I would keep the EdgeHD 8 and I would buy the RASA 8 instead of the Hyperstar 8 if you can spend the extra cash. The difference is ~$700 but it will be worth it.

 

The RASA 8 is a dedicated F2 astrograph with a larger illuminated imaging circle than the Hyperstar 8. Even my 4/3rd size 294 vignettes quite a bit with the C8 Hyperstar where as the RASA should have 93%+ illumination to the edge of this sensor.

 

Also since it is designed and optimized for imaging at F2 it should perform better overall vs. a Hyperstar setup with less pain. Collimating and aligning a hyperstar to a C8 is a hit and miss proposition. The RASA 8 should be aligned and optimized out of the box.

 

It also has a significantly improved focuser which is very useful for achieving and holding precise focus at F2 for long exposure imaging (I don't mean sub exposures but total exposure time).

 

I actually think $1700 is a very good price for a highly optimized F2 imaging system. My guess is it will be less pain more fun.


Edited by Astrojedi, 14 September 2018 - 01:50 PM.

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#35 calypsob

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Posted 14 September 2018 - 03:07 PM

That's not what I'm talking about.  The quality of correction of a Schmidt-corrected telescope varies depending on the separation between the Schmidt corrector and the primary mirror.  The spacing between the Schmidt corrector plate and primary mirror on commercial SCT's is actually sub-optimal (they are too close together to fully correct coma).  This is done to make the telescope a much more compact size.

 

In the RASA, they have placed the Schmidt corrector farther from the primary mirror, likely improving correction for coma and other off-axis aberrations.  In addition, wider spacing may be responsible for reduced spherochromatism, so the RASA has a wider range of wavelengths that it's well corrected for.

have never used hyperstar or a rasa, is a uv/ir cut filter required on either of these to eliminate star bloat on an osc camera? 



#36 evan9162

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Posted 14 September 2018 - 03:41 PM

If the OSC doesn't have a UV/IR-cut filter built in, then you'd need one anyways, regardless of telescope type.  There are some UV/IR-cut filters that block anything below 430nm (normally they pass down to 400nm) - those help with blue star bloat by blocking the deeper blue wavelengths.



#37 evan9162

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Posted 14 September 2018 - 07:33 PM

I would keep the EdgeHD 8 and I would buy the RASA 8 instead of the Hyperstar 8 if you can spend the extra cash. The difference is ~$700 but it will be worth it.

 

The RASA 8 is a dedicated F2 astrograph with a larger illuminated imaging circle than the Hyperstar 8. Even my 4/3rd size 294 vignettes quite a bit with the C8 Hyperstar where as the RASA should have 93%+ illumination to the edge of this sensor.

 

Also since it is designed and optimized for imaging at F2 it should perform better overall vs. a Hyperstar setup with less pain. Collimating and aligning a hyperstar to a C8 is a hit and miss proposition. The RASA 8 should be aligned and optimized out of the box.

 

It also has a significantly improved focuser which is very useful for achieving and holding precise focus at F2 for long exposure imaging (I don't mean sub exposures but total exposure time).

 

I actually think $1700 is a very good price for a highly optimized F2 imaging system. My guess is it will be less pain more fun.

 

There aren't a lot of systems that give you 400mm @ F2.  A 6" Boren-Simon astrograph (6" F/4 newt with 0.7x reducer/corrector) is roughly the same price, but is slower and smaller aperture - so less resolution.

 

I don't know if there are any astronomical refractors that can get that fast - but the next closest thing is the 400mm F/2.8 lens from Canon, which is a neat $10K.  

 

So for the aperture and speed, it's a pretty good value, assuming the image quality holds up....



#38 P_Myers

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Posted 15 September 2018 - 02:06 PM

FYI....the 8" Celestron RASA are meant to be used with the "mirror-less" DSLR cameras.



#39 bobzeq25

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Posted 15 September 2018 - 02:14 PM

FYI....the 8" Celestron RASA are meant to be used with the "mirror-less" DSLR cameras.

Or, even better, small round CMOS/CCD.


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#40 Astrojedi

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Posted 15 September 2018 - 02:56 PM

FYI....the 8" Celestron RASA are meant to be used with the "mirror-less" DSLR cameras.

Actually Celestron marketing blurb targets the new dedicated CMOS imagers and EAA applications as well.



#41 Omorali

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Posted 16 February 2019 - 02:43 PM

RASA

=====

"... Performs over a wider spectral range than most telescopes, from 390 - 800 nm.

So, more of the light passing through the astrograph is in sharp focus. ..."

 

Edge HD

=======

?

 

 

Q1) What is the wavelength range of a typical 8" Celestron Edge HD + Hyperstar ?

Q2) 390 nm is deep in the UV vs what for the 8" EHD + HS ?

Q3) 800 nm is deep in the IR vs what for the 8" EHD + HS ?

Q4) Will this be of any benefit for the typical astro-photographer?

This is more-or-less how I have evaluated the situation too. I own a plain C8 and will be getting the 8" RASA at the end of the month. I will be selling off my Hyperstar system and commit my C8 to planetary imaging.

 

I personally believe the 8" RASA has doomed the Hyperstar platform.


Edited by Omorali, 16 February 2019 - 02:44 PM.

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#42 RogeZ

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Posted 16 February 2019 - 06:14 PM

Where would one purchase a two piece Bahtinov Mask?


The 8" RASA Manual appears to be out.
https://celestron-si...5Lang_PROOF.pdf

Let me point you in the right direction

 

All of these scopes require dewshields, you then mount the bahtinov mask on the dewshield itself. I use a SpicaAFlat bahtinov mask on the C14HD in this manner.

 

My vote is RASA btw.



#43 lucutes

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Posted 17 February 2019 - 10:31 AM

This is more-or-less how I have evaluated the situation too. I own a plain C8 and will be getting the 8" RASA at the end of the month. I will be selling off my Hyperstar system and commit my C8 to planetary imaging.

 

I personally believe the 8" RASA has doomed the Hyperstar platform.

I think that's a bit of a stretch. Starizona have some great accessories and they could capitalize on the need for filter changers, RASA specific bahtinov masks (which btw nobody has made yet), power supplies, or even RASA specific filters. I once owned a C11 Hyperstar but heard there was a V4 coming out so I sold my V3, but then RASA 8 was announced. So far my issue in life is having to go out to dark sky sights and the C11 alone is quite the production. The RASA 8 could be a nice compromise and coupled with a IMX183 sensor I'd be curious to see the kind of resolution you could get compared to using a larger sensor with a bigger RASA or APO.



#44 Blade71

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Posted 27 February 2019 - 05:15 PM

I am also thinking of the RASA 8, I currently have an 8SE and a WO GT71 with a ZWO ASI183MC Pro for imaging. My concern is my mount, it's an AVX. I know it has a 30lb limit and with my add ons (guidescope w/ASI120MM-S,  telrad, and possibly a dew shield I'm reaching about 22-24 lbs. Am I pushing it with the AVX? I've seen an C11/AVX combo and the OTA was @ 27.5lbs, but I'm betting that was planned for only visual. Any thoughts?



#45 lucutes

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Posted 27 February 2019 - 05:59 PM

I am no expert but I’d bet if people use C8/Hyperstar combos on an AVX mount I bet an 8” RASA will probably be fine. At 400mm focal length it’s more forgiving. You can save weight by not using a dew shield and or heater and use a small guidescope. 


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#46 t-ara-fan

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Posted 15 June 2019 - 08:05 PM

 - but the next closest thing is the 400mm F/2.8 lens from Canon, which is a neat $10K.  

 

 

That lens is a beauty. I rented one for a weekend for $100.  FAST!  

 

Check out this pic at full resolution. Definitely sharp!!!   https://www.astrobin.com/410552


Edited by t-ara-fan, 15 June 2019 - 08:07 PM.

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#47 Lead_Weight

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Posted 17 June 2019 - 04:32 PM

I am no expert but I’d bet if people use C8/Hyperstar combos on an AVX mount I bet an 8” RASA will probably be fine. At 400mm focal length it’s more forgiving. You can save weight by not using a dew shield and or heater and use a small guidescope.


I bet it would work too. I used an RC6 that was 22lbs and reduced down to 915mm, it worked fine.

#48 bobzeq25

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Posted 18 June 2019 - 05:36 PM

I am also thinking of the RASA 8, I currently have an 8SE and a WO GT71 with a ZWO ASI183MC Pro for imaging. My concern is my mount, it's an AVX. I know it has a 30lb limit and with my add ons (guidescope w/ASI120MM-S,  telrad, and possibly a dew shield I'm reaching about 22-24 lbs. Am I pushing it with the AVX? I've seen an C11/AVX combo and the OTA was @ 27.5lbs, but I'm betting that was planned for only visual. Any thoughts?

Thoughts.

 

Lets assume you _could_ afford a better mount if you need to.  Yes, you're very much pushing it with an AVX.  The question is would it work?

 

And that depends on the specific AVX you have.  They're variable in quality, which is why their reputation is so mixed here.  People who got a good one just don't understand how frustrated people who got a bad one are.  I have utterly no idea what the proportions are, both are significant.

 

So a plan is to try it, with the idea that, if it doesn't work you'll get a better mount.

 

If that's not an option, I definitely wouldn't risk it.


Edited by bobzeq25, 18 June 2019 - 05:37 PM.


#49 TelescopeGreg

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Posted 18 June 2019 - 07:11 PM

What Bob said.  I have a Celestron 8" f/5 (f/5.6 with the coma corrector) Newtonian on my AVX, and with the guide scope, cameras, etc, etc. the load comes in at about 27 lbs.  It does work, but is absolutely pushing it, and I wouldn't recommend going that way.  Besides the weight limit, the AVX is not good for imaging targets that are very high in the sky, due at least in part due to the lack of a proper Dec bearing in the mount.  It's just not a high-end mount, and would not be a good match to a spectacular OTA such as the RASA.

 

The only thing going for you would be that the RASA's 400mm focal length is short and fast enough that you might get by with the less accurate mount.  I'm at 1,150mm, and at times the guide graph looks like I'm imaging from inside a bouncy gym at the county fair.  If you go for the Edge HD 8, in spite of how Celestron sells it, you're not likely to get good DSO images at f/10 or probably even at f/7, as the long focal length will magnify the inaccuracies in the guiding.  When Celestron talks about imaging, they're talking about planetary imaging, not DSO.  Big difference.  I made that mistake earlier...



#50 Blade71

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Posted 18 June 2019 - 09:37 PM

Thoughts.

 

Lets assume you _could_ afford a better mount if you need to.  Yes, you're very much pushing it with an AVX.  The question is would it work?

 

And that depends on the specific AVX you have.  They're variable in quality, which is why their reputation is so mixed here.  People who got a good one just don't understand how frustrated people who got a bad one are.  I have utterly no idea what the proportions are, both are significant.

 

So a plan is to try it, with the idea that, if it doesn't work you'll get a better mount.

 

If that's not an option, I definitely wouldn't risk it.

Thanks Bob and Greg, 

 

I decided to get the CGX mount, I bought a William Optics ZS126 and with that OTA weight, I knew the AVX wouldn't be able to handle it so pulled the trigger on the new mount and I just received my RASA 8 so that'll be going on it too. I'll keep my AVX for my smaller OTAs and for travelling. Thanks for the help. CS!! 


Edited by Blade71, 18 June 2019 - 09:38 PM.



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