Expert: Paul Wagner - 1/20/2007

Question
I'm hungry for aperture, and once had a good telescope (Celestron NextStar 11" SCT). But I had to sell it because my back surgery has restricted my weight limit. I'd love to have a dob of 12"-14" aperture, but I'm hearing that truss designs more easily lose collimation than tube types. And there are precious few used truss dobs for sale in my price range. But I did see a scope for sale, a homemade dob, that was a tube type - but was cut in half, reassembled and secured by trunk-type hasps or buckles. My question is: could I purchase a tube type, then have a machinist or other craftsman to bisect it and make it reassemblable in like manner? That would not only get the sectional weights down, but be easier to reassemble on the road. Is this practical, or even doable? I hesitate to try it myself. Any advice will be greatly appreciated. Thank you.

Answer
Hi Tom:

Absolutely!  The concept will work--although I think any time you move a reflector, you will have to re-collimate.  But that isn't a terribly hard thing to do.  Just get one of those laser collimators, and learn how to use it.  It will take a couple of times to get the idea, but once you do, it shouldn't talk you more than a few minutes to collimate---less time than it will take the mirror to cool down.

As for the technical aspects of your idea---You could easily have a good craftsman build some 1x1 rails that would slot into tracks on the other tube...it would be pretty darn stable and pretty accurate.  And those clasps would keep everything from moving around. Don't forget that this will probably change the center of balance of the scope a little bit...you may have to adjust the cradle an inch or two in one direction to compensate.  

But a 14" tube type scope is still going to be pretty heavy.  The mirror alone is going to be around 50 pounds, I think, once you put it in its cell.  The bottom part of the tube is still going to be work to move.  You might also look at building some kind of a dolly to move it around.  I've seen those work pretty well--and are a lot easier on the back!

Paul Wagner