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22" F4.0 truss dob design thoughts/questions

Started by dsummers, 08/16/2002 04:33PM
Posted 08/16/2002 04:33PM Opening Post
I've been dreaming about an ultralight 22" design that falls somewhere between a Greg Babcock design (look at his 24" ultralight) and an Obsession (which I currently own an 18" model of). I wonder why innovative design thoughts aren't gaining ground (why don't mirror cells pivot (tailgait) for easy cleaning of the primary mirror), and why aren't the altitude bearings attached directly to the mirror cell (eliminating most of the primary box/rocker assembly height). Does anyone know of a person/company that's on the leading edge of new ultralight large dob designs where the box assembly isn't the end-all design goal and feet-on-the-ground viewing is king? I'd love to find that company or forum to support. Maybe if a few of us were more forceful in driving design considerations, we'd have more choices. Large dob designs seem to be in a rut and in need of some creative engineering to get to the next breakthrough. Anyone want to offer an opinion of who's leading the pack in new design thoughts for the big ones? I'm stuck between capitulating for a smaller commercial scope than I want (due to the boxy designs), and making my own scope (which may be problematic while I work through issues to "get it right"). Ideas?
Posted 08/16/2002 07:03PM #1
Doug:

I posted a pic of my 16" f/4.5, but deleted it becasue I thought it might be viewed as an ad based on the "mood" of your post. My scope has no mirror box, the cell is the core of the lower end. The scope weighs 62lbs including the mirror. The rocker and ground board ~8lbs. It includes some other ideas that are proving to be very rewarding as well. I think I can shave a few more pounds off it as well. Done without exotics like CF or Foam core materials.

Al Highe has a line of scopes using three tubes that is very interesting and Litebox has done a fine job of re-engineering the typical Dob to a lighter more compact version. I was just at the OSP and Chuck Dethloff has made some simply stunning travel scopes that protect the sensitive componets of a scope during air flights. There is innovation. But the standard offerings are hugely successful, and I think for good reason.

So, I'd like to take a minute to defend the mirror box type scope your wondering about. There are many trade offs invloved in making telescopes and I think the offerings from the big guys repesents an excellent compromise on these trade offs.

For instance, setting up Greg Babcocks scope, or mine is not quite as hassle free as bolting four triangles to the mirror box as the Starmaster or Night Sky does. The mirror box provides protection for the primary that minimalist designs don't. Primary dewing is more easily control or headed of with the mirror box and secondary dewing with a full double ring UTA.

As for cooling, the current crop of scopes have fans, open backs, removable tailgates, etc. that don't seem to impede cooling efficiency. The full UTA of these scopes, coupled with there shroud provides maximum baffling against stray light from neighbors, street lights etc.

Let's face it, most of these scopes spend thier lives in the backyard of suburban neighborhoods. Once a year they travel to dark skies for a star party. Not all, but I would guess most. They're wheeled out of the garage already set up, to cool during dinner and observe. A home for the mirror so secure the cat can't even get in there for a nap! How big a factor is weight, or minimalist designs against sturdy, proven durablity and protection of the primay of the typical Dob to most folks? Considering the range of folks these are marketed too, and the range of mechanical ability, they represent an excellent product for the general high end market. How many times have you seen a post from someone that starts out like this, " I just recieved my new Starmaster 18" scope, and need help collimating it". You get the idea.

I am totally thrilled with my lightweight scope. Email me if you's like, I have a few pics, not very good, but I can take some more.

Steve Vegos
astro@rvi.net