Celestron 11" f/2.2 Rowe-Ackermann Schmidt Astrograph (RASA) optical tube

[alpal]

11" f/2.2 Rowe-Ackermann Schmidt Astrograph (RASA) optical tube.

see link:

https://www.astronomics.com/11-f22-r...be_p20206.aspx


What do people think about this new scope from Celestron?


F2.2 is very fast.
I wonder if you can use an OAG with it?

It would be nice if they published a large 4000 pixel wide frame of an image.

[RickS (Rick)]

They quote a 70mm image circle then only show vignetting and spot diagrams for a 42mm circle It will need a compact camera anyway.

Back focus is going to be very limited. Shame they don't give us the data in the specs. I doubt it will be possible to fit an OAG but at 620mm focal length a guide scope will be fine if the mirror doesn't slop around.

Will be interesting to see how the results compare to a Hyperstar set up.

Cheers,
Rick.

[gregbradley]

Looks interesting. Mirror flop may be something to know if its a problem or not.

The posted images are very small so its hard to evaluate them. The usual problem with very fast scopes is they are often hard to collimate and very susceptible to any flex. So that would be the thing I would want to see, how rigid is it, does it suffer from tilt/flex with bigger cameras?

Correctors tend to dew up. But it could be interesting. I'd like to see more sample images. F2.2 potentially sounds good and 11 inches of scope is a good size.

Greg.

[alpal]

Originally Posted by RickS

They quote a 70mm image circle then only show vignetting and spot diagrams for a 42mm circle It will need a compact camera anyway.

Back focus is going to be very limited. Shame they don't give us the data in the specs. I doubt it will be possible to fit an OAG but at 620mm focal length a guide scope will be fine if the mirror doesn't slop around.

Will be interesting to see how the results compare to a Hyperstar set up.

Cheers,
Rick.

Hi Rick,
Yes strange how they don't specify the back focus.
It seems like an alternative to the Hyperstar.
You're right - they don't show the spot diagram at 70mm.

As the premium end of the market has no such beast for sale at below f3
I have to seriously doubt the credibility of this telescope design.
Still - I have an open mind & I'm interested to see the results- one day.

cheers
Allan

[alpal]

Originally Posted by gregbradley

Looks interesting. Mirror flop may be something to know if its a problem or not.

The posted images are very small so its hard to evaluate them. The usual problem with very fast scopes is they are often hard to collimate and very susceptible to any flex. So that would be the thing I would want to see, how rigid is it, does it suffer from tilt/flex with bigger cameras?

Correctors tend to dew up. But it could be interesting. I'd like to see more sample images. F2.2 potentially sounds good and 11 inches of scope is a good size.

Greg.

Hi Greg,
someone will buy one & we'll all get to see the results.

cheers
Allan

[Camelopardalis (Dunk)]

A chap over on CN already has one, so we might not need to wait too long to hear initial feedback.

The RASA has mirror locks like the Edge HD series, so once you've got good focus you just lock it up...bye bye mirror flop.

[Satchmo]

Originally Posted by alpal

I have to seriously doubt the credibility of this telescope design.

Alan - Dave Rowe is the inventor of the Corrected Dall Kirkham cassegrain design ( CDK ) which is currently having tremendous success for its relatively fast speed and and wide flat coma free field. You can be sure that the design is exceptional - on paper at least . Whether it can be pulled off mechanically is another question , but as modern imaging can pull off modest length subs and refocus when necessary and the image scale is fairly modest I can't see how it would not work well.

[alpal]

Originally Posted by Camelopardalis

A chap over on CN already has one, so we might not need to wait too long to hear initial feedback.

The RASA has mirror locks like the Edge HD series, so once you've got good focus you just lock it up...bye bye mirror flop.

I can't wait to see the results.

[alpal]

Originally Posted by Satchmo

Alan - Dave Rowe is the inventor of the Corrected Dall Kirkham cassegrain design ( CDK ) which is currently having tremendous success for its relatively fast speed and and wide flat coma free field. You can be sure that the design is exceptional - on paper at least . Whether it can be pulled off mechanically is another question , but as modern imaging can pull off modest length subs and refocus when necessary and the image scale is fairly modest I can't see how it would not work well.

Celestron could also be using his good name for marketing purposes.

[gregbradley]

It looks like the camera is meant to be at the corrector end. That would limit the size of camera to be used. So the 70mm circle would be hard to
use. Perhaps a FLI Microline 16803 may work as its very compact.

Greg.

[alpal]

Originally Posted by Camelopardalis

A chap over on CN already has one, so we might not need to wait too long to hear initial feedback.

The RASA has mirror locks like the Edge HD series, so once you've got good focus you just lock it up...bye bye mirror flop.

Do you know under what name he posts at Cloudy Nights?

[Camelopardalis (Dunk)]

Coastal IIRC...have a look in the Cats and Casses section.

[alpal]

Originally Posted by Camelopardalis

Coastal IIRC...have a look in the Cats and Casses section.

Thanks - here is the link & he's posted a cropped photo of M13.

http://www.cloudynights.com/ubbthrea.../o/all/fpart/1


cheers
Allan

[raymo]

It does tell you the back focus. It says the back focus from the camera
adaptor is 55mm.
raymo

[RickS (Rick)]

Originally Posted by raymo

It does tell you the back focus. It says the back focus from the camera
adaptor is 55mm.
raymo

Silly me. I thought they might have listed it in the specs No room for any fancy accessories...

[alpal]

Originally Posted by RickS

Silly me. I thought they might have listed it in the specs No room for any fancy accessories...

Gee wizz - what camera , filter wheel & OAG can fit on that?

[gregbradley]

That's next to impossible. SX Trius, Mini SX filter wheel with built in OAG + Adapters is about 54mm that may work.

The Trius is 17mm to the chip from the lip of the camera.
The Mini USB filter wheel with OAG is 28mm
The 2 adapters on either side are about 9mm.
Then any adapter on the scope itself is an unknown. A Trius 814 would be good with this scope 9mp and high QE low read noise and small although the filter wheel is a bit large.

Probably best with a one shot colour and OAG.

Greg.

[Camelopardalis (Dunk)]

55mm happens to be normal for DSLR....

[MrB (Simon)]

Yeah, DSLR without an OAG...
55mm is rediculous.

[rustigsmed (Russell)]

yep camera at the corrector plate end, dslr, OSC or mono without filter wheel.
guiding? probably not - but do you need it?