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Hi Joe,
Regarding some of your questions:
* Holding collimation depends first on the quality of the primary mirror cell - If it is under engineered there'll be flex; if it uses sprins and they are undersized, they won't hold their position; if it is a truss scope and the entire OTA isn't rigid, then there will be flex issues and so collimation problems; if the secondary holder isn't held securely then again there will be issues. Many large mass produced Newtonians, from 10" up, be they solid tube or truss or strut, commonly have weak primary mirror cell springs.
* Where will you be keeping your scope at on the property. Unless these conditions are dry, regardless of the build quality of the scope, it will deteriorate, structurally and optically alike. Keeping it in a shed without any from of protection from big fluctuations in heat, damp, condensation, etc, it just won't last.
* Size is a concern. There are real practical reasons why mass produced big dobs stop at 16" - start going larger and there are both significant structural issues for the scope, are very heavy, and to keep both feet on the ground require very fast mirrors that are very expensive and difficult to make.
Glen has mentioned getting a GSO 16". These are very good quality wise for the money. Yeah, sure you can get a "better" primary, but are you doing research or enjoying the experience. A GSO will throw up a very good image. The other thing you can do is purchase the GSO and have a new scope built with the optics. You won't find cheaper good optics, and the new structure will not only perform better from considered design, but will last longer too. Alas the rocker box on all these mass produced dobs is made from terrible quality particle board that will distort when the poor seals in the melamine starts leaking dew into it.
Is there a difference between a Lightbridge and a GSO 16" - no. Other than some structural differences, optically they are pretty much the same for quality and collimation hold. As with any mass produced scope there will be those samples that are exceptional and those that are poor. But on a whole they are just as good as the other. Oh, and the rocker box of the Lightbridge is made of the same stuff as the GSO's are.
# A new player is coming soon onto the Australian market for custom built scopes. They will be offering ultra light dobs from 10" to 20", using materials such as carbon fibre for the poles and primary mirror cell components, that are totally Australian built and original in design. I can't say more than this right now, but keep and ear to the ground...
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