I recently built a 10" f5 imaging newt using carbon fibre strut design and plywood station rings. It is light and performs great. Have a look in the ATM section for my build thread and photos.
Thanks Glen. I'm looking for a cheap tube solution at the moment so CF is out of the picture (most of the funds go towards getting the Zambuto mirror).
Do you know any sources for a 12" or 14" OD, 1.5m long aluminium tube?
Probably the biggest issue with using the 12" tube is that the focusser will be pushed further off centre possibly requiring a slightly larger secondary mirror. That and the slight weight and diameter increase.
If it's a temporary situation till bigger and better arrive then I'd go ahead. Otherwsie you can still build a truss or Serrurier type OTA with alum tubes and ply. Quite a bit cheaper than carbon etc. Depends on how much effort and time you want to put in.
What is your intention with the scope, photo or visual? If visual, dob mount or eq?
While designs for both photo and visual require a rigid structure, the way you go about designing an OTA is influenced by the mount. Designing an OTA for a dob mount has different requirements to that mounted on an eq mount. Each style of mount subjects the OTA to a different set of forces, and makes different use of the centre of gravity.
There are also subtle differences in the way you set up the optics in a scope for primarily photo as to visual. This even influences the choice of secondary mirror for each, though at f/6 it is touch and go, so you need to make the appropriate calculations to determine this.
Glen came up with a very novel way of building a Newtonian for eq mounting. It is a very rigid design and makes use of ultimately a massive set of poles in a great 'cage' arrangement. By 'massive' I mean their collective rigidity is enormous in the way they have been arranged. For a dob mounted scope, it is would set the centre of gravity too high within the OTA and would need a very high rocker box to mount it. For an eq mounted instrument, this higher centre of gravity is a better suited. Different purposes brings a different set of requirements.
The scope is for visual only and will be on a dob mount and clamshell ring similar to the one shown in this picture http://astrogoods.com/007a.jpg
I re-ran the newt calculations using a 12" OD tube and a lower profile focuser and I think I can use a smaller 1.83" secondary while still maintaining at least 0.5" 100% illumination diameter.
