Please talk me out of this...

[Datalord]

I've been having immense fun with the RASA (as clouds permitted), but I'm yearning to do some of the smaller DSO's, which is obviously not what it was created for.

So I was looking at this: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p6512_TS-12-inch-f-8-Ritchey-Chr-tien-Astrograph---carbon-truss-tube.html

My CGX has a max load of 25kg and this one is 24. With the camera + OAG + stuff, I'd probably be pushing 26 kg. What are the chances this will go wrong? Should I put the upgraditis out of my head?

[Stu]

Isn't normal imaging practise to stay at around 50% of the load capacity? Seems like you need a bigger mount too  

[oldfruit]

Looks like re-mortgage time!

[mikeDnight]

DON'T DO IT!!!!!!!!

[DaveS]

Rupert from Astrograph and I touched on the RC12 at Astrofest and concluded that my DDM60 with 28kg payload for imaging would *just about* cope.

I'd be looking at a more capable mount than a CGX for 2.4m FL and 24kg.

[DaveS]

BTW the RC12 is available here from Astrograph.net.

[Datalord]

On 10/02/2018 at 20:50, DaveS said:

Rupert from Astrograph and I touched on the RC12 at Astrofest and concluded that my DDM60 with 28kg payload for imaging would *just about* cope.

I'd be looking at a more capable mount than a CGX for 2.4m FL and 24kg.

Hmm, so I should have gotten the CGX-L back then. Ultimately this is the only thing stopping me. I simply cbb to go through a change in the mount. The money is bad enough, but going through selling is the biggest pain. Any ships out there that would do a trade in?

[geoflewis]

52 minutes ago, Datalord said:

My CGX has a max load of 25kg and this one is 24. With the camera + OAG + stuff, I'd probably be pushing 26 kg. What are the chances this will go wrong?

The clue might be in the recommended mounts on the TS site - 'The telescope is perfect for small observatories and will be carried from mounts in the EQ8 class.' EQ8 mounts are rated for ~50kg payload, which fits with a rule of thumb that you should operate at ~50% of maximum rated payload. I think you'd be fighting all night long with that scope on your CGX. Just my 2 penniesworth....

Would be a nice scope though if you also upgraded the mount

Good luck, Geof

[DaveS]

If you only went to the 10", that's 15kg and 2m FL which should be much more do-able on the CGX.

It's not just mass, but FL and how well the mount will carry and guide it.

[Datalord]

2 minutes ago, DaveS said:

If you only went to the 10", that's 15kg and 2m FL which should be much more do-able on the CGX.

It's not just mass, but FL and how well the mount will carry and guide it.

Very good point. Somehow the 10" hasn't come up in my musings. That could settle it very quickly... 

 

[paulastro]

Datalord.  As per other folks' comments, I think you'd be taking a risk if you're intending to use your current mount.  You wouldn't want to be in the position that you buy the scope only to find your mount is inadequate.  Sorry to be a killjoy.

[Datalord]

On 11/02/2018 at 12:29, paulastro said:

Datalord.  As per other folks' comments, I think you'd be taking a risk if you're intending to use your current mount.  You wouldn't want to be in the position that you buy the scope only to find your mount is inadequate.  Sorry to be a killjoy.

Yeah, I think the solution is the 10". It's 5kg lighter than the RASA and 2000mm fl would be a good place for me. Almost pressed the buy button today. 

[Ikonnikov]

I have the altair 10" carbon fibre non truss tube version with upgraded focuser and it's just over 18kg with ccd attached, just light enough for my avalon linear mount to handle ok. 

For all but the lightest imaging train I'd strongly recommend getting a version where the telescope rear thread is not  attached  to the primary mirror (I bought a Moonlite kit for this but i think some vesions come with this modification already made) plus upgrading the stock crayford focuser (Im using a TS rack and pinion).

 

Paul

[Datalord]

10 hours ago, Ikonnikov said:

I have the altair 10" carbon fibre non truss tube version with upgraded focuser and it's just over 18kg with ccd attached, just light enough for my avalon linear mount to handle ok. 

For all but the lightest imaging train I'd strongly recommend getting a version where the telescope rear thread is not  attached  to the primary mirror (I bought a Moonlite kit for this but i think some vesions come with this modification already made) plus upgrading the stock crayford focuser (Im using a TS rack and pinion).

 

Paul

I don't get it, why would they attach the image train to the mirror? That makes no sense to me. 

[Ikonnikov]

4 hours ago, Datalord said:

I don't get it, why would they attach the image train to the mirror? That makes no sense to me. 

The focuser screws on to the back of the primary mirror cell in some of the GSO RC scopes, presumably as a cost/weight saving measure. Agreed it's dumb since colllimating the primary changes the tilt of the focuser unless you install an extra focuser tilting ring (in addition to having the weight of the imaging train hanging off the primary cell which still isn't fixed by instaling the tilt ring). The moonlite mod involves drilling holes in the back of the aluminium rear scope casing to bolt a new threaded attachment to it  so that the focuser etc hangs off this and not the mirror cell. Sounds drastic but I'm no craftsman and I managed it fine by following youtube video (once I sourced the obscure imperial drill bit required!). I'm pretty sure the 10" and up enclosed and truss tube designs had this problem but some of the newer TT scopes explicitly state they've been redesigned to incoporate this modification (I think the Teleskop Service 12" TT one mentions this but not sure about their 10").

Old discussion of this problem here for example

 

Paul

[Datalord]

That thread is a tale of horror and lost nights. Count me out of a GSO RC. What nonsense... 

Any other RC scopes <20kg I should look into? 

[Datalord]

Am I reading it right, that this scope has solved this exact problem? 

https://www.teleskop-express.de/shop/product_info.php/info/p6882_TS-Optics-10-inch-f-8-Ritchey-Chr-tien-Astrograph---carbon-truss-tube.html

[DaveS]

Looking at the TS site it looks to me as though the 12" RC has a decoupled focuser but the 10" doesn't. Not sure I'd want to dismantle a £3000 'scope to get it working as it should have when it left the factory.

Trouble is, if you want a RC "done right" then you have to pay serious money http://cfftelescopes.eu/reflector-rc250mm-f8/ .

[Datalord]

6 hours ago, DaveS said:

Looking at the TS site it looks to me as though the 12" RC has a decoupled focuser but the 10" doesn't. Not sure I'd want to dismantle a £3000 'scope to get it working as it should have when it left the factory.

Trouble is, if you want a RC "done right" then you have to pay serious money http://cfftelescopes.eu/reflector-rc250mm-f8/ .

Hmm, kinda cool. And light. The 12" weighs only 18kg. http://cfftelescopes.eu/reflector-rc300mm-f8/

 

What I was referring to with the TS was this: "The 3" Monorail focuser is a further development of the Crayford design. The load is not carried by four (often underdimensioned) ball bearings, but on a stainless steel track on the base, thus preventing tilting and bending even under high loads." 

" the base" is not the base of the scope? 

[DaveS]

I think they're referring to the design of the focuser. Looking at the photos and comparing with the 12" I don't see an additional set of screws for collimating the focuser independently of the mirror.

[DaveS]

Oh, and £7500 for the 12" is a bit more than the £3000 for the GSO .

[Datalord]

14 minutes ago, DaveS said:

Oh, and £7500 for the 12" is a bit more than the £3000 for the GSO .

Yep, but if it works... 

[Datalord]

47 minutes ago, Datalord said:

Yep, but if it works... 

Seriously, as Olly mentions in that thread, what matters is that [removed word] Just Works when you have the clear sky. I'm willing to pay good money for that. £3000 for something you have to drill holes in is just robbery, plain and simple. 

[DaveS]

If you can afford it, go for it. I do like the look of the CFF 'scopes.

[Ikonnikov]

I bought my Altair 10" second hand for half the retail price so wasn't quite so worried about drilling holes etc (although I did watch the instructional video about 20 times before doing the Moonlite decoupling mod!).  It would have been a different story if it was my (bought from new) Tak Epsilon though... 

On the plus side for the GSO-based scopes (including TS and Altair Astro derivatives) the optics are excellent and the quality of the tube construction is sound. The Moonlite flange is rock solid (which highlights the stupidity of GSO in not including this for a couple of extra bucks worth of aluminium in the original design) and the scope holds its collimation well after being lugged in and out of the house. After indoor collimation the scope was essentially seeing limited and I've taken test images with FWHM under 2 arcseconds  (which I didn't think my Yorkshire skies were capable of!). And even taking into account purchasing a decent rack and pinion focuser (~£300-500) and the Moonlite decoupling flange (~£125) you're still looking at only around half the price for the equivalent aperture CFF scope. 

Also (somewhat putting the cat amongst the pigeons once more) see this CN thread on the CFF RC250...

 https://www.cloudynights.com/topic/577046-cff-250mm-10-rc-arrived/

 

Paul