GSO RC rear cell design - 8in closed tube vs 10in truss - Forums

Topic starter

May 26, 2023 · Edited: May 26, 2023

Hi everybody,

I’ve been hunting to get a longer focal length telescope (900 - 1250mm) to image smaller targets for quite a while now.

Currently Im 90% sold on getting the TS ONTC - 8” F4.5 Newtonian… But I really like the idea of an 8” RC as well…

I do have an concern regarding the rear cell configuration on the 8in RC specifically to make my final decision.

I know of the collimation issue on this design due to the limited tilting adjustment due to the focuser / image train being directly connected to primary mirror cell. This can be addressed to some extend by installing a tilt adapter between the scope and the focuser if I understand correctly. However, it seems that the problem runs a bit deeper, in that a heavy image train can actually pull on / flex the whole primary cell, throwing off collimation. Has anybody here have more info on this?

As I understand, on the 10in Truss RC design, this has been solved by completely isolating the image train from the primary mirror cell.

I would be hesitant to invest in the 8in RC with this design limitation. The 10in truss with these issues sorted then seems to be the way to go, although for me personally, it might be just too much scope… Fully loaded at around 40pounds its closing in on my mount’s max load capacity (I have an SB MyT) and I dont really trust that I have the seeing conditions to support 1300mm-2000mm imaging regularly in any case.

Would love to hear your thoughts and experiences.

Regards,
Jacques

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andrea tasselli

Frequent contributor

May 26, 2023

Since you do not make a clear statement of what make/model you are talking about it is hard to make suggestions. Were I to make the choice I would go with the newt up to 12" (f/4). Beyond that it gets akward to manage without an pier and an observatory at hand. Modified DK are the way to with larger telescopes up to 20"-24", if you ask me. Beyond that you really need corrected RC.

jacquesdeacon

Topic starter

May 26, 2023

Thanks for the reply @andrea tasselli,

I have been looking at the TS-Optics 8” and 10” RC’s specifically, but If I understand correctly all offerings in this class is just rebranded GSO designs.

8” RC link:
https://www.teleskop-express.de/shop/product_info.php/info/p14982_TS-Optics-8--Ritchey-Chrtien-Pro-RC-Telescope-with-Carbon-tube---OTA.html

10” RC link:
https://www.teleskop-express.de/shop/product_info.php/info/p10815_TS-Optics-GSO-10--f-8-RC-Astrograph-with-carbon-truss-tube-and-focuser-tilting.html

Regards,
J

andrea tasselli

Frequent contributor

May 26, 2023

Between the two I'd go with the 10", better design IMO. But I'll take the 8"/10" ONTC over those any day, much easier life.

jacquesdeacon

Topic starter

May 27, 2023

Thanks again @andrea tasselli,

Yes, I guess in the end a Newtonian is just simpler to live with, and probably in my personal case, the way to go.

The RCs were attracting me because of the extra focal length reach, but I want to be careful to not over-stretch and run into issues above my capabilities, as I am also unfamiliar with reflectors.

Regards,
J

Rafał Szwejkowski

IOTD Staff

May 27, 2023

Thanks again @andrea tasselli,

Yes, I guess in the end a Newtonian is just simpler to live with, and probably in my personal case, the way to go.

The RCs were attracting me because of the extra focal length reach, but I want to be careful to not over-stretch and run into issues above my capabilities, as I am also unfamiliar with reflectors.

Regards,
J

I disagree that a Newtonian is simpler to live with, I think the opposite. The 10" GSO is a great telescope and free of the problems that you've mentioned. Absolutely worth it over the 8".

Well Written

Dave Bloomsness

May 27, 2023

I own a SB MyT and a TPO 10" Truss tube RC as well as a Skywatcher 10" f4 Newt. I had to rebuild the Skywatcher to make it a good scope at about 4 times the original cost. The ONTC would be a better choice. The MyT handles both scope very well, but I am permanently mounted on a sturdy pied in an Observatory. Might be different on a tripod. As for which is easier to "live with", I find the shorter focal length of the Newt a little easier for me, mainly because the seeing at my place is often not great. I also use the Starizona Coma Corrector / Reducer that let's me image at f3 with the Newt for a wider field. I have also used the Astro Physics CCDT67 Reducer with the RC for a focal ratio of around f6.
I like both scopes and although I'm not really stating a preference, I hope this info helps.

Dave

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jacquesdeacon

Topic starter

May 29, 2023

Thank you for the comments.

@Dave Bloomsness, yes my concerns as well. I think the MyT should be ok with an 10” telescope, set-up rigidly. My set-up is currently mobile (tripod), will get a tricky in less than ideal conditions, like unprotected from wind, cable-drag ect.

I think the 8” Newtonian is a good compromise, is more manageable and a good entry-point for me personally into the reflector game.

Regards,
J

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