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Celestron 8" RASA

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#1 Tattooeddeputy

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Posted 24 November 2018 - 03:36 PM

Hello...

 

Curious if anyone has ordered one of these.  Either recieved it or could answer a couple questions. 

 

Thank You



#2 bobzeq25

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Posted 24 November 2018 - 03:39 PM

They're not available yet.  Maybe not until January.

 

Your questions?



#3 Tattooeddeputy

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Posted 24 November 2018 - 03:45 PM

Just curious how difficult or easy too focus?  Also I use a qhy 168c APS-C size sensor and curious if this will be ok on it.

 

Thanks



#4 pyrasanth

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Posted 24 November 2018 - 04:03 PM

I would wait until you get solid reviews on this new model. There has been a lot of speculation about the available back focus which could be a limitation to what cameras can be bought to a focus. I certainly know that DSLR is not suitable and Baader are working on a set of adaptors which may or may not be part of the UFC series. If you can afford the jump- both in price & mount the 11" is a more flexible option.



#5 bobzeq25

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Posted 24 November 2018 - 04:08 PM

Focusing an F2 scope is never going to be easy.  They brag about their new focuser, although it's one speed.  I'll likely put a stepper motor on it.

 

Your image scale will be 2.4.  I've imaged at 2.4, I think it's fine.  Below is an example at 2.8.   Fullsize here.

 

https://www.astrobin...367734/?nc=user

 

Your exposures will be very short, unless you have very dark skies.  You'll probably need hundreds of subs.  The image below is about 100.

 

For the RASA I'm planning on a tiny pixeled 183.  Image scale 1.2, not as good signal to noise ratio.  Compared to your camera, mine is like changing the RASA to F4.  But, for equal total imaging times, I'll only be taking 1/4 as many subs as you.  Life is tradeoffs.  <smile>

 

NGC6992 HaO(III)RGB V1.jpg

 

Backfocus will be fine with a color CMOS camera.  Adding filters will be just a bit tricky, but doable, I think.  I'm planning on doing some H alpha.

 

The 11 was/is too heavy for this old man.  <smile>


Edited by bobzeq25, 24 November 2018 - 04:23 PM.

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#6 freestar8n

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Posted 25 November 2018 - 08:29 PM

Focusing an sct with a stepper on the primary knob is always “focusing at f/2” and I find it quite easy with automatic focus and backlash compensation. Nice repeatable focus curves and small fwhm.

If the rasa focuser is improved it should be even easier - but I see no negative impact of the normal focusing system. The curves and fwhms speak for themselves.

Frank

#7 lucutes

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Posted 28 November 2018 - 01:36 AM

I've got one on order. My first camera I will try is the ASI071, although not ideal. Next it's either my 1600MM or maybe buy an IMX183. The IMX193 would be better and APS-C but I might hold out for a filter changer and the ASI1600. The 1600MC would be a strong match for this scope as well but ZWO stopped making them... 



#8 Nicole Sharp

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Posted 28 November 2018 - 01:47 PM

Saw this on Celestron's website.  Looks exciting, but isn't it basically the same as an EdgeHD 8 Hyperstar?  At least with the Hyperstar, you have access to both short and long focal lengths, so you can use it for both deep-sky and planetary imaging.



#9 George N

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Posted 28 November 2018 - 01:49 PM

I'm surprised that Celestron doesn't 'bundle' one of their own astro cameras with the RASA 8, with a discount to encourage a duel purchase.

 

They do provide some pretty good info on the RASA 8 webpage (https://www.celestro...trograph-rasa-8) covering recommended cameras - and noting what cameras it does not work well with.



#10 DonBoy

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Posted 28 November 2018 - 02:03 PM

Saw this on Celestron's website.  Looks exciting, but isn't it basically the same as an EdgeHD 8 Hyperstar?  At least with the Hyperstar, you have access to both short and long focal lengths, so you can use it for both deep-sky and planetary imaging.

Here is the designers take on the 8" RASA

 

https://www.cloudyni...a/#entry8851753


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#11 Nicole Sharp

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Posted 28 November 2018 - 02:18 PM

Here is the designers take on the 8" RASA

 

https://www.cloudyni...a/#entry8851753

EdgeHD 8 Hyperstar is 390/203 with a 76-mm central obstruction and a 28-mm image circle, whereas the RASA 8 is 400/203 with a 93-mm central obstruction and a 22-mm image circle.  Also, the RASA 8 weighs 17 pounds when the EdgeHD 8 with HyperStar weighs 15 pounds.  Looks like the EdgeHD 8 Hyperstar should outperform the RASA 8 in pretty much every regard?



#12 Nicole Sharp

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Posted 28 November 2018 - 02:21 PM

I think the main attraction would be the price.  The EdgeHD 8 with HyperStar is $2248 MSRP whereas the RASA 8 is $1699 MSRP.  But you are going to get vignetting with an APS-C (27-mm) sensor on the RASA 8, whereas no vignetting with the EdgeHD 8 HyperStar.


Edited by Nicole Sharp, 28 November 2018 - 02:26 PM.


#13 gomezdb

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Posted 28 November 2018 - 02:50 PM

I think I will wait until Celestron decides to release the RASA 9.25

 

Clear skies,

Diego



#14 DonBoy

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Posted 28 November 2018 - 03:15 PM

I think the main attraction would be the price.  The EdgeHD 8 with HyperStar is $2248 MSRP whereas the RASA 8 is $1699 MSRP.  But you are going to get vignetting with an APS-C (27-mm) sensor on the RASA 8, whereas no vignetting with the EdgeHD 8 HyperStar.

The Hyperstar 27mm image circle is not fully illuminated and is probably the same equivalent illumination level image circle of the 8" RASA of  32mm.  So would suspect that there would be less vignetting with the 8" RASA for APS-c size sensors, but still vignetting.  The 22mm fully illuminated image circle of the 8" RASA should work well with the the 1600 cmos sensor cameras.   We'll have to wait and see how this all plays out.



#15 WadeH237

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Posted 28 November 2018 - 03:52 PM

I think that the 8" RASA also has a zero image shift focuser (possibly the system designed by jhayes_tucson on Cloudy Nights).  The EdgeHD 8 has the old focuser design.

 

That difference alone would make the decision for me, if I were primarily interested in doing F/2 imaging with one of these scopes.  It's possible (ok, so I am just hoping) that the RASA has a better collimation system than Hyperstar, since the entire OTA is purpose built for F/2 imaging.

 

I have done Hyperstar imaging with a C8 and APS-C sized chip.  It is *incredibly* unforgiving for collimation of the front lens and tilt in the primary mirror.  If I take the time to get round stars in the corners in one area of the sky, and then do a meridian flip to the other side, the corners are messed up again.  I've pretty much switched to a refractor for all of my wide field imaging.  It's not as fast, but it is a *lot* easier if you are really picky about the stars in the corners of the field.


Edited by WadeH237, 28 November 2018 - 03:57 PM.


#16 Astrojedi

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Posted 28 November 2018 - 10:28 PM

EdgeHD 8 Hyperstar is 390/203 with a 76-mm central obstruction and a 28-mm image circle, whereas the RASA 8 is 400/203 with a 93-mm central obstruction and a 22-mm image circle.  Also, the RASA 8 weighs 17 pounds when the EdgeHD 8 with HyperStar weighs 15 pounds.  Looks like the EdgeHD 8 Hyperstar should outperform the RASA 8 in pretty much every regard?

Actually the opposite... the RASA is a purpose built F2 imaging system. It does one thing only but does it really well. Having imaged with both Hyperstar and 11” RASA... the RASA was painless in comparison with much better image quality.

 

- Does not need OTA specific collimation like the Hyperstar (which is a PITA)

- Very stable collimation and better thermal characteristics

- a better more precise focuser - in the new 8”

- Larger illuminated imaging circle


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#17 Kaydubbed

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Posted 29 November 2018 - 07:04 PM

According to lucutes - who has done more research on the RASA 8" than anyone else I have seen on CN - there might be QA issues causing delays. I wouldn't be surprised if the release is pushed to Q1 2019. That being said, I canceled a pre-order in favor of a fast 80mm APO. I have a ASI071 and the image circle + not being able to use a Bahtinov mask + all the other quirks of collimation, cable management, and filters made me rethink it. 

 

That being said, if I do get another scope, I WILL be looking at you, 11" RASA. 


Edited by Kaydubbed, 29 November 2018 - 07:05 PM.


#18 lucutes

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Posted 30 November 2018 - 03:35 AM

According to lucutes - who has done more research on the RASA 8" than anyone else I have seen on CN - there might be QA issues causing delays. I wouldn't be surprised if the release is pushed to Q1 2019. That being said, I canceled a pre-order in favor of a fast 80mm APO. I have a ASI071 and the image circle + not being able to use a Bahtinov mask + all the other quirks of collimation, cable management, and filters made me rethink it. 

 

That being said, if I do get another scope, I WILL be looking at you, 11" RASA. 

"Not being able to use a Bahtinov mask?" It's easy. Put it on the end of a dew shield.


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#19 George N

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Posted 01 December 2018 - 01:58 PM

….... I wouldn't be surprised if the release is pushed to Q1 2019. ….

Just in time for those NEAF discounts!  cool.gif 



#20 Phil Cowell

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Posted 01 December 2018 - 07:56 PM

Just in time for those NEAF discounts!  cool.gif

An 8” RASA would make a nice compliment to my 11” RASA.


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#21 akulapanam

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Posted 01 December 2018 - 11:36 PM

The problem is this thing has such a limited FOV and so little backfocus that only OSC is practical, not really a step up from Hyperstar like the 11" RASA is.  Good intro to astrophotography scope though.


Edited by akulapanam, 01 December 2018 - 11:36 PM.


#22 RogeZ

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Posted 07 December 2018 - 06:37 AM

Im sure mono is doable as well. Just install the filter in the camera adapter. Done.

#23 lucutes

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Posted 07 December 2018 - 11:14 AM

Im sure mono is doable as well. Just install the filter in the camera adapter. Done.

 

I checked with Celestron. There is no 2” threads on the inside of the adapters. I need to put a UV/IR-cut filter on for my OSC so I ended up ordering their RASA 8 LPS filter. $$$.

I hope they sort this out because even QHY doesn’t have UV/IR coatings on their versions. 


Edited by lucutes, 07 December 2018 - 11:16 AM.


#24 Tattooeddeputy

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Posted 23 January 2019 - 11:21 PM

Bobzeg25....do you have the 8" rasa and a qhy168c? Wanna pull trigger but hope my camera will be ok

#25 lucutes

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Posted 24 January 2019 - 09:50 PM

Bobzeg25....do you have the 8" rasa and a qhy168c? Wanna pull trigger but hope my camera will be ok

QHY168C is the ASi071MC I think and that is what I am planning to use. Hopefully some warm clear weather ahead.




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