In 1995 The St. Petersburg Astronomy Club acquired a 17.5in mirror. The board of directors of the club
asked me to build a scope around it in time for their annual star party in early 1996. This is
the result.
The scope was built in only 3 months. In spite of the fact that it was a rush job, it turned out very
well, and has survived 5 years of very hard use including long road trips to Texas and Arizona. It is
used several times a month at the many public events held by the club.
The scope was designed to be as portable as possible for such a large instrument. Here it is broken
down and ready to go up a ramp into a minivan. The secondary cage nestles into the rocker box. The
truss tubes are in the long black bag. The toolbox holds the Telrad, 60mm finder scope, and a few
other bits. No tools are necessary for setup or breakdown.
This photo shows the process of cutting the large circular opening in the plywood octagons that make
up either end of the secondary cage. This is done with a plunge router with a homebuilt circle
cutting jig attached.
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Here is a photo of the secondary cage sitting on my table saw shortly after assembly and before
finishing. The two octagons are the only moderately difficult pieces to make. Everything else is
just straight cuts.
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Here the secondary cage has had a sheet of Formica cut to size and installed inside as a light-weight
light baffle. The inner surface was painted black during finishing.
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This is a look inside the completed mirror box before finishing. At the bottom is the 18 point Kenneth
Novak & Co primary mirror cell. The 8 "U" clamps for the trusses are also visible.
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This outside view of the mirror box shows one of the Kenneth Novak & Co altitude bearing rings
mounted on the side of the box. On the inside you can see the six mounting bolts for ring on the other
side, as well as another view of some of the "U" clamps.
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Here is the completed rocker box before finishing and adding bearing hardware.
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Here is the ground board that the rocker box sits on and pivots around.
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Here is a detailed shot of one of the upper truss clamps.
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Here is the new and improved 17.5 inch Dobsonian Scope. It got a complete remodeling and refinishing. It now looks brand new again and
a little more modern I think.
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Here is a closeup of the remodeled secondary cage. I made a lot of changes up here. Probably the most obvious change is all the holes
I cut in the wood to lighten it. Lightening the scope was one of the main goals of this remodeling. For every few ounces shaved off the
secondary cage meant I could take pounds off the main mirror box.
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Here is another view of the secondary cage. Aside from the Swiss-cheesing of the wood to save weight, I also replaced the original Formica
light baffle with a sheet of very thin and light oak wood veneer. I also ditched the Telrad I had been using and replaced it with a tiny red-dot
sight. It's not as easy to use as the Telrad, but it is a lot lighter.
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On the rocker box I cut off unnecessary corners and cut holes in the structure to lighten it. All together the modifications shaved over 25
pounds off the weight of the telescope. It's still a very heavy scope, but every little bit of weight savings helps my back.
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Another modification I made was to cover the Aluminum trusses with black heat-shrink tubing to darken them. It's a lot better looking than
the black duct tape I had been using before. I also refinished the small refractor finder scope. I think the scope really looks great, but I
may be a little biased.
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As the first big outing for the newly remodeled scope, I took it out to my property in rural Arizona. I spent a week out there observing under
the pristine Arizona sky. It was a great time and the scope worked like a champ.
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Here is a photo of the big Dob set up at the Orange Blossom Special Star Party in February 2006 at the Alafia State Park.
As you can see, it is decked out with all its accessories, including its matching wooden finder scope
and its heavy-duty equatorial platform.
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Another photo of the big scope at the OBS Star Party. It got a lot of use during the four nights I was there.
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