I guess I should have guessed some of my wordy posts, even with some bad grammer are actually read by some people out there. To show you how tired and on the run I've been, someone at last months club meeting metioned they heard I was thinking about a 20 inch dob project and I wondered where they heard it from. It was only after reviewing some of my posts here (and shaking my head a little at how bad my writing is. . . ) that I realized I had mentioned a 20 inch mirror for sale on Astromart in my blog. They must be reading this blog.
You have to remember I'm a dreamer and like to dream about gadgets. I dream perhaps about 20, maybe 200 or even 2000 gadget dreams before trying to actually make one. I can dream and imagine a lot, and save on perspiration (old fashion Edison work ethic) by leaving them in dreamland.
This weeks dream includes thoughts about the little 8 inch mirror I bought either for a little toying around or to have the kids at the school play with. The other day, I was thinking about creating some kind of unique and super light mono-body construction Dob. Something more like a monoframe, that held a mirror box. Sort of like an open mount. Kind of like a ("telescope man") Harold's example telescope that uses a simple board.
But instead of a board it would be more like a contructed body. Perhaps one sculpted in foam at first, like a Recumbent racing bike. Then covered in Carbon fiber for strength, like the body of a Carbon Fiber low racer. Carbon fiber would give it a killer look. I'm not saying it would be some kind of James Bond combination of a telescope and bike or something like that. That of course would be going to far. Perhaps adding a wheel kit and bike chain and sprockets would be going to far. Althought it's be interesting to say, I drove my telescope to the meet. But that's for another post and a more heavy design session.
It might have a primary and secondary box attachment and it could hold a mirror box of some kind. The secondary attaches to one end with the eyepiece and finder, like modern dob designs. It would be a monotube body with the rings and mirror boxes free floating on one side of it. Of course would have to be fairly rigid. Perhaps hoops could be designed to hold a shroud, for city viewing. Without the shroud it would make a pretty killer demo piece with a completely open design, but of course in a real field it would allow a lot of dust into the telescope and on the optics.
Then my imagination starts to go a little more extreme. How about making it a dual configuration kind of thing, maybe add a place for a second mirror that would slide in or attach some how with a different secondary or spider. Maybe two secondary cage configurations that would swap in and out. One closer to the primary which would be tilted. Perhaps the primary mirror box would have two slots to fit into and one would tilt it slightly. This would create a Dobsonian with two eyepiece and secondary positions. The first position, furthest from the mirror in standard conventional Newtonian position would be a full mirror setup with a regular spider. The second position would use a mask and the mirror would be offset. The top secondary cage might even be removable for this second configuration. In either case, the second configuration would tilt the mirror and a mask would be added to the front.
FOLDED NEWT DESIGN CONFIGURATION (configuration 2)
We'd be using half the mirror or a circle allowing light in. For the 8 inch this would be a 4 inch circle perhaps. It would reflect off half the shrouded mirror and back to an offset diagnal with the second focuser which is further back. This makes the dobsonian an offset Newtonian that is masked. Why do this? It creates a light path that doesn't have a secondary or spider at all in the light path. It's a "folded Newtonian" design in the second configuration. Basically a fully corrected clear 4 inch telescope with no color issues (like refractors) and no secondary obstruction. This is the kind of design you'd want to have to use for planetary viewing. If you don't have $10,000 for an expensive APO from Takahashi, you can perhaps build a folded Newt and have some pretty nice planetary results. Hmm. A F7.5 masked 8 inch becomes a F15 4 inch in this configuration. Sounds like a pretty cool planetary focal length design.
So I'm thinking in the second variation (of course I've had more thoughts) that if I was going to get radical with some kind of carbon fiber design, why not go further and get two scopes out of one body. Of course with designing and planning any added thing may add options, but take away others. For example adding more options and features by expanding the frame of the scope and how it works, adds weight. You have advantages and disadvatages to each design idea, which is what happens in the real world. In snowmobile design for example which changes each year, some came up with the thought of reducing parts to make the sled lighter and design each part to do many functions not just one. So a successful light design would use fewer parts. Or would require more swapping of mirror cell layouts and retain only one eyepiece and secondary in either configuration. You might have one primary mirror box and two secondary cages. One with the mask and folded optics. If both were seperate the collimation of the secondaries would be rather quick and might not require much work. If you were really good in you're design you might have some kind of adjustable tilt stops with fine adjustments to setup a tilt and tune colimation of the primary to happen with a fairly simple tilt and few adjustments to go from one mode to the other, but that's asking for a lot.
If you make it some kind of massive scope with both secondaries and focusers on it and somehow have the folded one swing into the light path when in folded mode, you've added a lot of weight to the original Carbon fiber idea. Different designs have advantages and disadvantages. Some of course just use a shroud over their Newt to make things simple. That might be the quickest solution, but you may lose a little bit of primary mirror size, due to the secondary being in the way, size compared to a true folded design with a different secondary that removes the regular one or shifts it somehow. (I'm not a fan of shifting one secondary with this design, because it would likely require more secondary collimation each time you switch modes.) If you really had the big bucks and had some kind of robotic secondary adjustment using lasers and computer controls or something like that, well then that takes my simple design and put's it into really hgih priced territory.
So I'm left with possibly going back toward a simple minimalistic design of one type to make it really light and have an advantage of using it on a cheaper lighter capacity mount or put in other cool features, but then needing a more expensive and heavier mount to use it.
Of course a million other ideas can come out of this. For example the body could have the mounting bracket built in for mouting it to a telescope mount. A built in dovetail in the sculpting of the Carbon fiber monotruss would allow you to mount it without an external bracket, just mount it to the Carbon Fiber. That of course makes it less flexible but lighter.
Then of course some would argue what's the best design and most rigid. How big would the monobody have to be to keep flexture down and why not just use light carbon fiber truss poles instead.
There's a lot of different options you might have. You might even fail without the truss poles and have to add them later. If you designed the main support frame strong enough it might handle different size mirror boxes with different sized mirrors. I could build it so it could expand. Start with an 8 inch and then add a different 10, 12 or larger mirror to it later, with a bigger mirror box and different secondary cage, the same monoframe might be workable for a range of telescopes.
Then I start thinking about that 20 inch mirror again.
Of course I could just go out and spend the money on a VK1 lowrider from Velokraft Poland and ride off into the sunset instead. Before I bore you with more dream variations it's time to sign off.
http://www.jjscozzi.com/VK1.htm - link if you want to see what a Velokraft racer looks like.
Greg K
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