Questions re: GEM to Dob conversion

I currently own a 10-inch f/4.5 Newtonian reflector on a GEM. I ground the mirror under the tutelage of Dan Joyce, who has an outstanding reputation (and deservedly so) for his mirrors. Dan is from the Chicago area, is a regular at Astrofest, AL conventions, and the Winter Star Party, where he teaches a mirror making workshop each year.

Since my observing style depends largely on a Telrad and star hopping, I've come to regard my heavy equatorial mount as overkill. As a result, I am toying with the idea of finding a telescope craftsman who would be willing to convert my telescope to a truss-tube Dobsonian. Since I ground my own mirror, I want to keep my primary mirror, but all other components are negotiable in terms of "keep" vs. "replace." But I have a few questions, as follows:

1. Besides the minor inconvenience of viewing objects near the zenith, are there any downsides to converting from a solid tube GEM to a truss tube Dobsonian?

2. So far, I've only found two telescope craftsmen who specifically advertise that they perform telescope conversions -- Teeter's Telescopes (Jackson, NJ) and Starsplitter (Thousand Oaks, CA). Are there any others?

3. Has anyone out there seen examples of both brands and can compare and contrast their workmanship? Please note that I'm most concerned with quality of construction, smoothness of motions, and professional appearance. I don't care about their optics since I will be using my own.

Thanks in advance for any advice I receive.

Bart

Bart,
Until I realized I had bit off more than I could chew, I owned a Teeter truss. Workmanship was excellent. Rob Teeter I believe is highly regarded, and a totally nice guy to boot. The difference I felt between the truss and the tube newt I have is that with the truss I had to tweak the collimation with every set up and take down. It as usually close, but not quite. With the solid tube I don't have to do this as often. When I was picking up the Teeter truss in NJ, I got a looksy at one of his dob tube conversions. Very nice work. There are other makers that create tube conversions and not just truss dobs, however. There's E2 and Firstbase that both make dob mounts.

Bart,

You may also want to look at Astrosystems in LaSalle Colorado. http://www.astrosystems.biz/.

They do a very nice job. The cost is less because you put it together yourself. They will also finish the work for you if you prefer. I believe at least one person has a review on Cloudy Nights. I have seen several of their finished scopes (including a real nice 32") and they are top notch. No, I don't have one yet, but I most likely will go with them because they are only 40 miles from my home.

Michael

Hi Bart,

I shopped around for a dob conversion of my Meade 10" SN. I got numbers in the range of $400-500.

Yes they were works of art, but I wanted to try out the idea first to see if I like the scope that way.

Last May, I was at RTMC and saw a fellow with an old style pipe mount (he later won a merit award), and I was inspired. So I visited the hardware store, and spent $39, and in literally one hours time I had this mount. OK it looks it too but with a second iteration, + paint, and a rotating base with teflon etc., it should work very well. I am able to use the scope quite easily even with the small base.

The tools needed to build this mount, are a drill and screwdriver.

Sincerely,

David Simons


PS. The military aircraft spotting bino's and this wide field scope are a wonderful combination.

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Bart,

Anybody who took on grinding a mirror should have the patience and personality to make a good dob mount for it. I don't think you should go anywhere else but to yourself to make the conversion.

The easiest conversion would be a square box whose inside diameter was the outside diameter of your current tube. Put a couple of bearings on the outside of that box, and the tube inside. Make a rocker box with trunions, and an azimuth bearing, and you will have your dob.

And, I would not go to a truss tube. The only two advantage of a truss tube over a solid are the open air--which could help cooling, and the portability.

As for open air, a better way, overall, is to install a fan (which would probably be a good idea on a truss tube anyway).

As for portability, that means really transportability, not just what car it will fit in, and so forth. A 10 inch F4.5 just does not take up enough room to change over to a truss tube--which would then require tight fittings, a lot of machining, repeatability in setup, and more collimation. You would spend less time transporting a tube than a truss telescope. You just don't have a big enough scope there to need truss tubes.

Alex