second scope

[hobbit]

Hey guys. I'm looking at getting a second scope to complement my ed120. The two that I've been looking at are
1) GSO RC8 (which is cheaper) and
2) Celestron 9.25 (which is bigger)

both are as big as i can go to keep in my mounts weight limit.

has anyone one tried both of these for a comparison?

[dannat]

is it for long focal length imaging or visual

[Logieberra]

Might be pushing it - but the 10" GSO truss is a beautiful thing. I have the 12" and couldn't be happier :)

[hobbit]

daniel, mainly imaging but will probably end up doing a bit of visual with it as well.

logan, unfortunately that's over the weight capacity of my mount.

[Logieberra]

The Vixen VC200L is also a performer. Another option perhaps?

[Chris85]

What mount are you rocking?

[hobbit]

celestron avx
I've heard that the vixen can be a real pain to collimate properly compared to other scopes. Is this correct?

[brian nordstrom]

:thumbsup: Go the 9 1/4 inch Celestron , you wont be disappointed one bit .
Mine is a real performer in all ways , awesome scopes .
Brian.

[Logieberra]

I've heard that too. Then again, search images from 'rmuhlack' :)

[5ash]

9.25" is great, came in the box collimated , have never had to collimated it. In comparison , the Newtonian and RC would need regular attention.
Philip

[hobbit]

hmmm....
Another thought has just occurred to me.
keep my mount and refractor as is.
Get a RC12 and EQ8 and stick them out at itelescope. I have considerable light pollution here anyway and I'm already spending more than I should be to rent scope time with them.
As logan says. That 12" RC is a thing of beauty.

This plan certainly escalated quickly

[gregbradley]

RCs and Dall Kirkhams are not good visual instruments usually having quite a large secondary obstruction.

But they are much better than SCTs for imaging. A 10 inch carbon fibre RC would be a very good imaging instrument although the focuser may need to be replaced unless you are using a lightweight camera. I checked out the 12 inch at Bintel and its an impressive scope except for the focuser which you can flex by hand easily. Still that is a well known issue with these GSO RCs but the optics are very good and I have been continually impressed with the quality of images they are producing. Plus the dielectric coatings have very high reflectivity, don't scratch and the carbon fibre truss seems very high quality.

A 12 inch GSO RC with a Sony 694 or a KAF8300 chipped camera would be capable of a lot. It would need an off axis guider to cope with the long focal length guiding.

Greg.

[LewisM]

Re VC200L collimation.

It's not particularly difficult, in fact, easier than an RC by a fair amount. Good thing about the VC200L is once it is spot on, it'll stay there indefinitely unless you bump the snot out of it. Vixen's collimation guide is good, especially the visual collimation guide. Vixen recommends NOT to use a laser.

I have only had to collimate a VC200L once, and I have had 4. It took roughly an hour to get pot on, using eyeball collimation. With the laser, you end up chasing your tail too much.

[Hans Tucker]

I disagree.
The Mewlon 250S I had, which is a Dall-Kirkham design, was a very good visual instrument. Granted the central obstruction of the secondary was 28% but this is significantly smaller than the 40% + the RC has.

[gregbradley]

Yes you are right I forgot about the Mewlons. I was referring to the current CDK type Dall Kirkhams with the corrector meant for imaging and using a larger secondary. Like Planewave and others.

Greg.

[brian nordstrom]

Yes , the Mewlon's awesome 1/20th wave guaranteed mirrors ,, Strong Japaneese build quality :thumbsup: yes , my old M210 gave the best 'Refractor' like images from any reflector I have ever looked thru up to 800x on a good night , but ,, yes there is always a but and here it is for me .:( .

Diffraction spikes , , for me I would personally put up with CA on a good Achromat ( iStar ) , hence I sold that awesome scope and now have an easy 96% of the Mewlon's quality of Luna / planatery views in my sweet C9.25 XLT starbright that I have now , and zero diffraction spikes :scared3:.

Brian

[Paul Haese]

Ah, the what is better question.

For what it is worth here are my observations from someone who has owned both scopes listed.

The 9.25 was a great scope and performed very well for planetary imaging with occasional viewing. Very light and had a good light grasp. The central obstruction made for contrast affected views but the detail was sharp. The corrector plate is and can be an issue in areas where dew is heavy. You need to have a dew system that can and does produce irritating tube currents. It is one of the banes of this design and as such I would not use this type of scope as a remote scope. Collimation is a breeze albeit you can be on your knees a lot during the process. These scopes now come with a flat field and reducers are made by the company. Though I don't see many pin sharp images taken with these scopes. I think the star sizes are still a problem and mirror flop is an ever present issue for the design despite locking pins etc.

The RC8-RC12 are good imaging scopes. I have spent a bit of time looking through them and would say the central obstruction does affect performance for viewing. I have looked through a Mewlon too and can say that while stars are refractor like, the contrast levels in RC's are significantly reduced over other types such as a refractor or Newtonian. However, imaging through this type of scope can and does produce great images. Collimation can be a pain and you are best advised to obtain a Tak Collimation scope to ensure you get the collimation right. Using a laser will not work as well if at all. Also you will need a dew heater in the secondary assembly to prevent dewing of the secondary. Also getting a flattener or reducer to work properly with a large sensor is going to test your patience. A 2" flattener will not work with a 11002 sensor and GSO does not make its own flatteners for this scope type. I am still trying to sort a 3" flattener. Overall the images produced by this design are very sharp and detailed.

For me the choice between the two designs is easy. The RC design is an easy winner. The mirror flop and corrector issue is more than enough to not own another SCT for DSO imaging.