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Celestron rasa 8 inch

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#1 Yamaha-41

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Posted 05 September 2018 - 01:12 PM

Hello, I've been a member for a while but this is my first post. Just curious if anyone has any information about this new scope. I currently have an edge 8 with hyperstar and I'm pleased with the pictures I get. I don't know if this new scope would have any big advantage over the hyperstar. Any thoughts?



#2 einarin

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Posted 05 September 2018 - 01:15 PM

I'm not aware of 8" RASA. Just 11" and 14".



#3 Yamaha-41

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Posted 05 September 2018 - 01:18 PM

Saw it today on celestron's site. 8" Rasa for $1,699.00


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#4 Xeroid

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Posted 05 September 2018 - 01:37 PM

Link:

https://www.celestro...trograph-rasa-8



#5 dustyc

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Posted 05 September 2018 - 02:35 PM

Well, you can't look thru it. At least with the Hyperstar you can remove it and revert back to a visual scope. Plus you have a option of 3 focal lengths with your present scope. F2, F7 (with reducer) and F10.  



#6 WadeH237

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Posted 05 September 2018 - 03:22 PM

I love the idea of the RASA, and the 8" is a great addition to the lineup.

 

There is one thing, though, that keeps nagging at me...

 

The short focal lengths on these scopes put them squarely in the wide field imaging category.  The thing is that wide field imaging benefits greatly from narrow band filters.  But the design of the RASA (and Hyperstar) really favors one shot color cameras - which rules out (or at least makes less efficient) narrow band imaging.

 

I have a C8 Hyperstar and had a C14 Hyperstar for a while.

 

The reason that I don't have the C14 Hyperstar any more is that I did not have a one-shot-color camera.  My ST10 with filter wheel worked fine on the C14, except that the filter wheel was only 5 position, so would not support full RGBHaOIIISII without removing the camera and replacing the filters.  Also, the accuracy of the filter wheel, combined with the vignetting at F/2 resulted in vignetting that shifted a significant number of pixels each time the filter changed, and this vignetting could not be properly flat fielded out (since it moved from frame to frame).  I ended up trading the C14 Hyperstar for the C8 Hyperstar because I really wanted a wider field anyway, plus I made enough extra in the trade to mostly fund a one-shot-color camera for the C8/Hyperstar setup.

 

And the reason that I don't use the C8 Hyperstar much is that I find that I don't have a lot of targets that I want to shoot that don't benefit from adding narrow band data.  And so for my wide field work, I use an 80mm refractor at F/4.8.  This gives me a very slightly larger field of view and longer exposure times - but I can use a camera with my full set of filters.

 

I'd be tempted to get an 8" RASA, except that I'm afraid that I wouldn't use it much and would continue with the refractor.  Is there something about these scopes that I'm missing? 


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#7 JoeR

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Posted 05 September 2018 - 05:50 PM

The short focal lengths on these scopes put them squarely in the wide field imaging category.  The thing is that wide field imaging benefits greatly from narrow band filters.  But the design of the RASA (and Hyperstar) really favors one shot color cameras - which rules out (or at least makes less efficient) narrow band imaging.

Not sure what you mean by less efficient. It's quite easy and effective to shoot narrowband with the Hyperstar. I have them for both the 14" & 8" and they work well with the Baader 2" NB filters when using the Starizona filter slider. Their filter slider can also be adapted to the RASA systems. Neither system can be automated with mono cameras which is definitely not an issue for me as I prefer to do everything manually.

 

What is unclear is whether Celestron has their new focusing mechanism for the 8" that they have on the 14". That would make it worthwhile as the $1699 price point makes it considerably cheaper than an EdgeHD 8 + Hyperstar + Feathertouch focuser. 



#8 Yamaha-41

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Posted 05 September 2018 - 06:35 PM

I assume like with the 8 inch hyperstar you couldn’t try a dslr with this rasa 8?

#9 cuivienor

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Posted 05 September 2018 - 06:48 PM

Wow... there goes my money... And yes, it does seem to have the new focus system: "NEW Ultra-Stable Focus System – six precision sealed ball bearings virtually eliminate image shift."


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#10 akulapanam

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Posted 05 September 2018 - 10:38 PM

I assume like with the 8 inch hyperstar you couldn’t try a dslr with this rasa 8?

It would block quite a bit of light even if it supports the image circle. I loved my Hyperstar but personally the 8” is pretty limited in actual application. If you can afford it the Tak e180 and Rh200 are better here. The 11” and 14” is a different story because of huge cost difference and support for bigger cameras and corrected field.

I do hope the focuser is added to the 11”

Edited by akulapanam, 05 September 2018 - 10:45 PM.


#11 WadeH237

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Posted 05 September 2018 - 10:54 PM

Not sure what you mean by less efficient.

By less efficient, I mean that you need to manually change filters, which means that you need to be there to manually intervene when the filter needs to change.
 

Neither system can be automated with mono cameras which is definitely not an issue for me as I prefer to do everything manually..

And there's the difference. I'm fully automated.

I do agree with you about the focus mechanism. The 8", at this price point, makes it accessible to most of us. For F/2 imaging at 400mm focal length, it's an incredible scope.  I just find that I'm doing a fair amount of LRGBHaOIII these days, and not being able to automate it is a showstopper for me.



#12 akulapanam

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Posted 06 September 2018 - 12:18 AM

By less efficient, I mean that you need to manually change filters, which means that you need to be there to manually intervene when the filter needs to change.
 

And there's the difference. I'm fully automated.

I do agree with you about the focus mechanism. The 8", at this price point, makes it accessible to most of us. For F/2 imaging at 400mm focal length, it's an incredible scope.  I just find that I'm doing a fair amount of LRGBHaOIII these days, and not being able to automate it is a showstopper for me.

With the 11" or 14" you can absolutely use a QSI camera. The 8" is a bit too small.



#13 cuivienor

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Posted 06 September 2018 - 01:55 AM

The 8 inch looks like an ideal match for an ASI294MC - fast focal ratio, big pixels (but not quite undersampled either), large FOV, big well depth, very high QE/sensitivity. Now with that, one second exposures could actually do the trick for many brighter objects and lucky imaging for DSOs is really within reach.


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#14 Astrojedi

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Posted 07 September 2018 - 09:11 AM

I agree it will be a good match for the newer color CMOS sensors including the 294. I used the 294 with the C8 Hyperstar and there was quite a bit of vignetting at the corners which was quite hard to correct from my light polluted location. It looks like the RASA 8 has a larger illuminated field based on the specifications on the Celestron website so should do better. 


Edited by Astrojedi, 07 September 2018 - 09:15 AM.

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#15 rockstarbill

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Posted 07 September 2018 - 09:46 PM

By less efficient, I mean that you need to manually change filters, which means that you need to be there to manually intervene when the filter needs to change.

And there's the difference. I'm fully automated.

I do agree with you about the focus mechanism. The 8", at this price point, makes it accessible to most of us. For F/2 imaging at 400mm focal length, it's an incredible scope. I just find that I'm doing a fair amount of LRGBHaOIII these days, and not being able to automate it is a showstopper for me.


It also only has 25mm of spacing, so it's pretty limited. Bummer.

#16 jhayes_tucson

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Posted 08 September 2018 - 01:19 AM

I love the idea of the RASA, and the 8" is a great addition to the lineup.

 

There is one thing, though, that keeps nagging at me...

 

The short focal lengths on these scopes put them squarely in the wide field imaging category.  The thing is that wide field imaging benefits greatly from narrow band filters.  But the design of the RASA (and Hyperstar) really favors one shot color cameras - which rules out (or at least makes less efficient) narrow band imaging.

 

I have a C8 Hyperstar and had a C14 Hyperstar for a while.

 

The reason that I don't have the C14 Hyperstar any more is that I did not have a one-shot-color camera.  My ST10 with filter wheel worked fine on the C14, except that the filter wheel was only 5 position, so would not support full RGBHaOIIISII without removing the camera and replacing the filters.  Also, the accuracy of the filter wheel, combined with the vignetting at F/2 resulted in vignetting that shifted a significant number of pixels each time the filter changed, and this vignetting could not be properly flat fielded out (since it moved from frame to frame).  I ended up trading the C14 Hyperstar for the C8 Hyperstar because I really wanted a wider field anyway, plus I made enough extra in the trade to mostly fund a one-shot-color camera for the C8/Hyperstar setup.

 

And the reason that I don't use the C8 Hyperstar much is that I find that I don't have a lot of targets that I want to shoot that don't benefit from adding narrow band data.  And so for my wide field work, I use an 80mm refractor at F/4.8.  This gives me a very slightly larger field of view and longer exposure times - but I can use a camera with my full set of filters.

 

I'd be tempted to get an 8" RASA, except that I'm afraid that I wouldn't use it much and would continue with the refractor.  Is there something about these scopes that I'm missing? 

 

The big advantage of the RASA and HperStar systems is the optical speed; but, I agree that they are not easy to automate for use with filters. That's the same weakness as the original Schmidt camera.  You really have to go OSC with these things if you want remote automation and that's why I got a refractor for wide-field remote imaging.  The good news is that with a good OSC camera, you can still grab some amazing images with these fast scopes in record time.

 

John


Edited by jhayes_tucson, 08 September 2018 - 01:21 AM.

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#17 CrossoverManiac

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Posted 12 September 2018 - 05:08 PM

According to the link, the RASA 8" is incompatible with a DSLR.  Does anyone knows why?



#18 Astrojedi

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Posted 12 September 2018 - 05:19 PM

A large DSLR creates a very large central obstruction on the 8”. The 8” Hyperstar suffers from the same issue.


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#19 CrossoverManiac

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Posted 12 September 2018 - 05:25 PM

So the camera goes where the secondary mirror goes?

#20 Astrojedi

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Posted 12 September 2018 - 06:02 PM

Yes, here is a image: https://cdn.shopify...._570x380@2x.jpg


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#21 CrossoverManiac

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Posted 12 September 2018 - 06:23 PM

What do they do about the USB and 12V cooler power supply cords?  Some of the DSLRs can be controlled with a wifi connection and all of them are battery-powered but the RASA 8" is not made for those cameras.



#22 akulapanam

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Posted 12 September 2018 - 10:24 PM

What do they do about the USB and 12V cooler power supply cords? Some of the DSLRs can be controlled with a wifi connection and all of them are battery-powered but the RASA 8" is not made for those cameras.


You run them over the primary , ideally in a horseshoe shape

#23 JoeR

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Posted 13 September 2018 - 08:11 PM

I have a 3D printed cable router for my 8" and 14" OTAs they work well. You can also make one from a simple wire armature. It just needs to form a 180° arc from the edge of the secondary obstruction to the edge of the OTA's retainer ring.



#24 pyrasanth

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Posted 20 September 2018 - 03:49 AM

I have the 11" RASA although it is not being used currently until I get another mount for it as the C14 is now the permanent fixture. I use the Baader UFC system in entirety and it is really superb. It is easy to change a filter if your with the RASA but the problem would be at a remote site if you wanted to do anything other than OSC or mono imaging.

 

Worth considering as an alternative to the Starizona filter slide https://www.baader-p...r-changer).html


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#25 jhayes_tucson

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Posted 20 September 2018 - 10:04 PM

According to the link, the RASA 8" is incompatible with a DSLR.  Does anyone knows why?

 

There probably isn't enough distance between the mounting flange and the focal plane.

 

John


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