Not really sure what you are asking here Brendan. Do you already have the optics or are you starting afresh.
Reason I ask is that I have had a 10" f5 optical set for yonks, and this same set has spawned a multitude of tube reincarnations. The latest C/F tube you saw is just one of many, believe me, LOL.
Now in the weight savings class, the biggest weight in my case is the primary, it is 5 kilos alone.
So, if you are starting from scratch look at the conical designs out there, Royce being one. In my mind (and limited tooling as well), they are simplest to attach to a cell.
If you already have the optics then you are sort of stuck, and really can just build what you are suggesting, truss possibly, or solid but light single piece tube.
From the archives, I built this hair-brained middle of the night design up, worked OK too, but it now resides with a friend (I think).
I have other pictures, and certainly hair-brained ideas if you feel the need to delve deeper.
Really, with my limited tooling, and basic skills, it wasn't that difficult. With the tooling and skills I perceive you have it will be a breeze.
Gary
So, if you are starting from scratch look at the conical designs out there, Royce being one. In my mind (and limited tooling as well), they are simplest to attach to a cell.
You can probably get away with bonding a thinnish 10" standard profile to a simple 6 or nine point cell with RTV and not have any edge clips.
Im not buying a 16" mirror just yet.... Its my current 10" newtonian the mirror is approximately 25-30mm thick and is approximately 3kgs. the skywatcher tube sucks badly its extremely heavy and adjustments are poor for the accuracy im looking for. the tube+mounting rings are nigh on 19kgs WITHOUT anything else
If i run the 40d+ed80 and all the other prafanalia that goes along with it im looking at close to 23kgs on the eq6 this is bad!
Im also looking to reduce the cross sectional area that breeze can act on.
gary, why did you vere away from the truss tube design?
Brendan
23kgs?? Heck, no wonder you are on the skinny it down bandwagon.
I am about 11kgs and that is with a F/T and 5 kilo primary.
The C/F truss was something I dreamed up, tried and then relinquished to a friend who was after a tube system for a 10" mirror. I will ask if he still has it, as the basics were sound.
In the end a truss needs a shroud, either for dewing purposes, or stray light purposes, and this just provided a big sail area. It worked, but the simplicity of a single solid tube was too good to pass up. And it didn't really come at a weight penalty either.
Gary
Im not to worried about putting a light shroud around the truss system i fully expected something like that to be the case. Pulling it taught should eliminate most of the sail area.
With the SW tube being already reasonably short at about 950mm and the fact that i want to gear it up for CCD+filter wheel in the future the tube will be even shorter.
Im not sure what the tube is made out of though i belive its thin steel.
how hard is CF to fabricate how expensive? I could be convinced to move the CF way if the price was right.
Not too sure I agree that the sail area is less when you pull it taut, being light (relatively) and with all that "sail" means any wind moves it about. If you are in a total dark area, the truss without would be fine.
If you have a tube ~950 long you are quids in, mine is a tad over 1200mm.
C/F is simple, it is just a poncey fiberglass really. It is a cloth that needs resin, simple as that. In my case I used an old sonotube tube that I parred the outer layers off, reducing the thickness by perhaps 3 - 4 mm, and attached the layer(s) of C/F cloth to the cardboard tube directly.
The cost (here) was about NZ$150 for the cloth, and about $70 for the resin, add more for disposable gloves, sacrificial paintbrushes etc.
CF truss was different, I purchased the 22mm tubing direct and cut it to length as required this being easier than the solid C/F tube.
Gary
that might be the way to go then, if we are talking sub $200 then ill put my hand to it. come to think of it the 4th year students over in the civil eng test facility are for ever putting carbon fibre on beams trying to get them to work better!
Might go talk to them! full CF tube for ~ $200... and light as light can be. that sounds like a winner to me!
Edit...
Just went searching for cloth, 1070 wide 200gsm CF cloth 87 dollars per meter! sweet! looking at this i might be even able to get the tube down to sub 2kgs now im thinking this is good!
Well, if you have others already using the stuff, go see what the lot of you can conjure up, it isn't really rocket science.
To make it completely lightweight you will need a former or mandrel, and then probably a couple of layers. This was one of the reasons I used the cardboard, albeit less than what I started with, it gave me something to work from.
Gary
Brendan did you think about folded optics such as a Nasmyth, Yolo or Schiefspielger deisgns that would reduce your overall tube length and subsequent weight
Not at all trev, the reason is i would have to change a hell of a lot of things to make it work properly if not change figures on the mirror add differnt mirrors in.
I work on the KISS principle. the tube isn't long as it is and with the additional focuser spacing that i want to gain so that im not sitting on the boarderline if i wish to add a ccd+filter wheel. it should be sub 900mm at the end. im happy with that!
Ok Brendan just a though as I believe the Nasmyth design is somewhat underated and underused
In fact does not require the primary to be reconfigured and you would only need one additional fixed mirror.
Oldham Optical Astro Page The extra cost of the elliptical flat is not significant when the cost of the other two mirrors is considered.
If the elliptical flat is towards the primary end of the tube, there are no extra optical obstructions and as an extra bonus, the baffling needed in standard Cassegrains is not required.
Stray light has a lot more difficulty in reaching the focal surface with this design.
Effectively halving the length of your optical tube.
now im thinking this is good!
