GSO RC10" first thoughts

[Hagar (Doug)]

I received my new RC10 last week and finally got a little bit of sky to take a look at. (That has now gone.

My first thoughts on the scope:

Again like the 8" it is built to a price. I spent the extra dollars and bought the carbon fibre tube version and like the 8" the carbon fibre serves no purpose other than to make it look good. It comes with a top and bottom losmandy plate which are securely fixed to the main mirror cell at one end and to the cast aluminium ring which supports the secondary mirror at the other end. With this tupe of fixing you could never ever call the carbon ring a zero expansion joint.
Like the 8" the focuser is pure rubbish. Yes it's bigger at 3" and stronger with much heavier material in it's manufacture but the support for the focuser draw tube is exactly the same as the 8" version in all aspects.
One big improvement is the addition of a center spot on the secondary mirror making collimation so much easier.

It does look good and initial trial image shows real promise but I will have to do some work on my mount to get the OVision worm working at it's best as at 2.0m focal length guiding errors are very noticable. It is a big scope and I mean very big and quite heavy to go with it's size.

I have ordered a new focal reducer which has yet to be tested and a nice new 3" feather touch focuser which should make this scope sing.
The initial starfield image shows real promise considering I had the Tak Field flattener just shoved in the imaging train at a distance way shorter than the desired distance.

Overall I think this should prove to be a very nice scope but should you be thinking of one as an imaging scope be prepared to add an extra $900au for a 3" FT focuser and somewhere around the $600Au mark for a field flattener and unless you want a nice black scope just buy the Aluminium version at $1000 less then add the extras.

Maybe I will get some sky to look at after the focuser and FF arrive or am I being hopefull.

[Octane (Humayun)]

Doug,

Thank you for being our guinea pig. I will wait with anticipation for your first light.

My true love lies in long focal length astrophotography, but, up until now I've been at a loss on what to get (read: save up for).

Since you have the same chip as I do, it'll give me a lot of food for thought.

I kind of expected that the focuser wouldn't be up to the task (especially having to carry an STL) and that about $1K would be required for a nice Feathertouch.

Eagerly awaiting!

H

[renormalised (Carl)]

For the initial outlay on one of these scopes, I would expect the focuser and such to be up to par and not having to be replaced. That would turn me off considering purchasing one.

[Hagar (Doug)]

Originally Posted by renormalised

For the initial outlay on one of these scopes, I would expect the focuser and such to be up to par and not having to be replaced. That would turn me off considering purchasing one.

I know what you are saying Carl but still think the purchase is still quite a bargain with respect to purchasing a similar sized RC. The biggest downside of doing it this way is that the dedicated gear that comes with the likes of the Deep Sky Instruments RC10 all fits and works and this way it is up to me to get it all together.

The cost of the DSI RC10C is something like $7000US + delivery and so far I have spent $5340 AU in total so there is a significant saving overall, It's just now up to me to make it all work and at this stage it is a somewhat unknown. A risk I am prepared to take.

[JethroB76 (Jeff)]

They should offer them sans stock focuser (as an option at least)

[allan gould]

Doug
I have been seriously thinking of going down this path but with the Al tube. Ill be watching this closely.

[Moon (James)]

Doug,
I'll be interested to see how you go with the new focuser and focal reducer. I think you're on the right track opting for the larger focal reducer - although it will be a bit of work to get all the adaptors and spacing right.
James

[gregbradley]

When you say there is no gain using the carbon fibre tube over the aluminium - are you saying the focal point isn't stable with temp shifts?

That is the usual reason for carbon fibre tubes - so the focus stays stable even with falling temperatures.

Aluminium typically should mean focus will be shifting as temps fall and will require refocusing on a regular basis. Not true with this model?

Greg.

[Hagar (Doug)]

Originally Posted by gregbradley

When you say there is no gain using the carbon fibre tube over the aluminium - are you saying the focal point isn't stable with temp shifts?

That is the usual reason for carbon fibre tubes - so the focus stays stable even with falling temperatures.

Aluminium typically should mean focus will be shifting as temps fall and will require refocusing on a regular basis. Not true with this model?

Greg.

I fully agree Greg. The fact that both mirrors are held by, in effect 2 big lumps of aluminium focus shift will happen. The shift shouldn't be that great with Al having a thermal coefficent of 23.
I do have similar concerns for carbon fibre rods etc used in telescope making due to the fact that the carbon fibre has a very low thermal co-ef but the epoxy resin it is held solid with is another matter entirely and without knowing the make up of this resin it is dificult to know what expansion and focus shift can be attributed to the resins used. The woven scrim of carbon fibre used is designed to allow for some expansion without breaking the carbon fibre strands which have a very low shear strength.
I think the difference between the carbon fibre and Aluminium model of this scope will be very negligable in fact probably very hard to measure or confirm that any difference at all exists.
A scope like yours which has the secondary supported entirely by the carbon strutts may be a different kettle of fish. Time and experience will tell in both cases.

The GSO optics look pretty good on an initial quick image and star test so for the price I am very happy.

[multiweb (Marc)]

Good for you Doug. I agree 100%. If you want to splash the money and have the red carpet straight out of the box you can but a little tinkering with what you got and improve it goes a long way. These RC clones are not cheap but you still pay for quality optics. Focusers, etc... are easily interchangeable.

CF is a good idea. I should receive one for my C11 next week too. Should make a significant difference. I don't know what your CFZ is but on the C11 the first few hours in the night are a killer when the temp drops. This tube shrinks like crazy. Need to refocus every 30min until the alu tube stabilizes.

[RobF (Rob)]

Interesting read Doug. I'd love to hear more as the adventure progresses - as will other dreamers here too I'm sure

[Bassnut (Fred)]

Yes, ive often wondered what effect the AL mounting rails had. My RCOS tube has the rails mounted on al clamps , one at the primary mirror end and the other about half way up the tube, I wonder if the clamp allows minor expansion due to temp?. The secondary mirror is mounted directly to the tube further up. I dont have focus shift problems at all.

The RCOS truss OTAs have rails hard mounted along the short tube (al?) part before the final CF truss connected to the secondary, I dont think they have focus drift either.

The CDK looks to be all CF, the short tube part and both truss sections, but again, the tube part is hard connected to an al rail.

As you say, it makes you wonder why they bother with CF tubes at all, unless the clamps are designed to allow "slippage"

[Alchemy (Clive)]

Interesting.......

I will start with my thoughts on the 8 inch, firstly it can produce an exceptional image, but I have seen very few in reality, from memory the earlier ones suffered from internal reflections, Pauls m16 was probably the best I saw, no one really put it to good use ( I can be corrected here as I spent some time away from IIS) other than a few bright image objects, it just didn't see the light of day..... I guess my question is why didn't anyone shoot faint galaxies with it?.
The imaging train is a complete horror with it extending waaaaaaaay back, given this is supposed to be an imaging scope it seemed a lack of design thought.
Onto the 10 inch, going by your critique, it has obvious design flaws, again it's obviously built to a budget, but when you have to throw away 1/3 of it's value just to get it up to usability.... I strongly suspect it can produce a very sharp image, but will anyone persevere with it ? I know the other scope mentioned is dearer, but you have been around for a while now and tried all sorts of gear, you will wish eventually thats the one you bought. Quality comes at a high price but thats what is most pleasurable to use.

I hope you take some great images with the new scope and give it ( to me anyway) a far better report.

I watch with exceptional interest to see what you can do with it.

[Hagar (Doug)]

Originally Posted by Alchemy

Interesting.......

I will start with my thoughts on the 8 inch, firstly it can produce an exceptional image, but I have seen very few in reality, from memory the earlier ones suffered from internal reflections, Pauls m16 was probably the best I saw, no one really put it to good use ( I can be corrected here as I spent some time away from IIS) other than a few bright image objects, it just didn't see the light of day..... I guess my question is why didn't anyone shoot faint galaxies with it?.
The imaging train is a complete horror with it extending waaaaaaaay back, given this is supposed to be an imaging scope it seemed a lack of design thought.
Onto the 10 inch, going by your critique, it has obvious design flaws, again it's obviously built to a budget, but when you have to throw away 1/3 of it's value just to get it up to usability.... I strongly suspect it can produce a very sharp image, but will anyone persevere with it ? I know the other scope mentioned is dearer, but you have been around for a while now and tried all sorts of gear, you will wish eventually thats the one you bought. Quality comes at a high price but thats what is most pleasurable to use.

I hope you take some great images with the new scope and give it ( to me anyway) a far better report.

I watch with exceptional interest to see what you can do with it.

Hi Clive, As you are probably aware I had an 8" version and to be honest it didn't get a whole lot of use and once I purchased the 11002 CCD I found the whole imaging thing with the little 2" focuser to be more effort than it was worth. Again I still maintain the optics were very pleasing but the same overall faults were evident in the 8". I really didn't come into this one totally blind of the faults and was prepared to purchase the extras required to get it all working.
To be perfectly honest I have yet to purchase any scope which has fitted it's designed purpose 100%. Some adapters , focuser upgrades, be it a robofocus unit or some extra glass. The FSQ is the best so far and even that didn't come with the adapters required to use the extender or reducer even though the scope was ordered from the factory with a matching set of glass.
The big upgrade for me was the 10" model comes with a 3" focuser and should accommadate the full frame CCD better.

[Hagar (Doug)]

Originally Posted by Bassnut

Yes, ive often wondered what effect the AL mounting rails had. My RCOS tube has the rails mounted on al clamps , one at the primary mirror end and the other about half way up the tube, I wonder if the clamp allows minor expansion due to temp?. The secondary mirror is mounted directly to the tube further up. I dont have focus shift problems at all.

The RCOS truss OTAs have rails hard mounted along the short tube (al?) part before the final CF truss connected to the secondary, I dont think they have focus drift either.

The CDK looks to be all CF, the short tube part and both truss sections, but again, the tube part is hard connected to an al rail.

As you say, it makes you wonder why they bother with CF tubes at all, unless the clamps are designed to allow "slippage"

It's a hard one to quantify Fred. I had a little Vixen VC200L which was all aluminium and never shifted focus from one week to the next. It was a ripper but again needed a focuser upgrade and some thinning of the secondary spider. Time will tell.

[bert (Brett)]

Originally Posted by Hagar

It's a hard one to quantify Fred. I had a little Vixen VC200L which was all aluminium and never shifted focus from one week to the next. It was a ripper but again needed a focuser upgrade and some thinning of the secondary spider. Time will tell.

Off topic sorry, but some one might find the info useful.

My vc200l is carbon fibre truss. The other factor is the strength of the aluminium itself, the vc200 tube has a tendency to flex even with full mounting rings.

Even the scope with a carbon fibre truss moves a little under temperature shifts. I use a fli focuser with absolute encoding, and focus max and I have found over extreme temperature (10-15 degrees c) drops I get a focus shift of around 50 steps which is around 200 micron, given that the cfz is 188, it is not too much of a problem as getting temp shifts of that range is rare.

Personally, I cannot say for sure, but I do not think it is the primarily the carbon fibre moving (I have stainless steel truss end clamps as well), but movement of aluminium imaging train, the corrector and mirror contraction.

I'm wondering given the differential of contraction between aluminium and carbon fibre, whether you will have stresses forming fom the carbon fibre tube and the 2 dovetails?

And Doug, please post some images with the rc soon!

Cheers
Brett

[Doomsayer]

A number of CF double (serrurier style) RC truss designs such as A&M had an expansion joint where the main dovetail saddle plate connects to the middle aluminuim plate section and the rear plate section. Because the rear of the actual truss is CF there can be some effects I gather.

All of the CF truss assemblies I have built are like the RCOS configuration - which basically has honeycomb aluminium in the rear section and a CF truss in the front section. The rear cage is very rigid and can carry big loads. Focus seems to be stable in my 12"RC, even though it uses a pyrex mirror.

There was a 20 inch RC on a Cloudy Nights ATM (?Preston) thread a year or two back which utilised the double truss config. It was a very sophisticated design - seemingly very similar to the A&M truss design, and it had some sort of expabsion joint or similar at the saddle plate.

Re: flatteners
My 12RC uses a simple 2.7" doublet field flattener - these came from Star Instruments - who also made the mirrors. They supplied me with the lenses and I had the lens barrel made to suit. These cover an 11k chip nicely and are supposed to cover the 16803. So the 'build it yourself' option can work. Using the 2.7" threaded AP extension tubes to house the lenses is another option.


guy