This is my first attempt to build a Dobs using a Serrurier truss design. I found the article Flexure of a Serrurier Truss, February 1994, Sky and Telescope invaluable. So far it has proven to be very stable. After aligning the optics with an autocollimating eyepiece in early fall of 1995, I find it is still in near perfect canceling alignment in late winter 1996 after much usage. The downside of the open design is the direct light path into the eyepiece from neighboring light sources. I plan to wrap the upper portion of the struts with a black nylon cloth.

I do not have a dome and yet I do not want to wheel the 'scope outside from the warm house. Barely discernible behind me is the closet which houses the scope when not in use. (My wife, Kathy, says it looks like an outhouse when it is closed. I agree enough to consent to her painting a half-moon on the door.) When the scope has been wheeled out, a shelf can be folded down at a convenient height to form a handy work space for charts. There is also a storage bin along the back which holds eyepieces, an LED flashlight and alignment tools.

I have a sort of a minimalist attitude towards my own private observing. I design and build automated telescopes fitted with first-rate CCD cameras professionally. But at home I like to use just an eyepiece and star-hop around to find things. On the other hand, I am considering mounting a small compass and elevation gauge to the rocker box so, in conjunction with a watch and a hand-held calculator loaded with a few equations, I can do some basic dead-reckoning when I get lost in sparse areas of the sky.

I have recently added a Star Site unit power finder. For those of you not familiar with this device, it is basically just an open tube with a ring of phosphor around the inside on the far (sky) end. There are no optics. The idea is to occassionally charge the phosphor with a light source then site through the tube, keeping the lit ring centered in the tube with no vignetting. I learned of this device in the unit power finder reviews in the June 1996 issue of Sky and Telescope.

I mounted the Star Site about 4 inches above the eyepiece -- not so close that I hit it with my glasses but close enough that I can use it without getting off the step stool. It only weighs a few ounces and did not effect balance. Having no optics, fogging and dewing are non-issues. The initial alignment was rather sensitive but once set it has remained stable. I found it worked best for me when viewed from about 10 inches behind (the instructions suggest 14). From there it subtends about 3 degrees of sky. I found my home-made LED flashlight was just barely adequate to charge the phosphor light ring on a dark night; when the Moon is bright I must use a white flashlight. An important thing to train yourself to do is find a spot on the telescope tube on which you can lightly place your head for a steady reference. Then focus on the sky with both eyes open and move everything (scope, star site, your head) as one solid unit. It look a little practice to get comfortable doing this but now I can position on a bright star to well within less than one degree. Overall, I am completely satisfied with the Star Site. It required 6 weeks for delivery.

Here are the basic telescope stats:

• Primary mirror: 18" parabolic, 2" thick, f/4.5, from Galaxy Optics
• Cell: 18 point flotation, from Novak
• Secondary: 3.1" flat (purchased, but don't recall from whom)
• Spider: 4 vane, from Novak
• Focuser: 2" low profile, Tectron
• Eyepiece: 26mm, Meade Series 4000 Plossel
• View: 79x, 40 arc minutes
• Finder: Star Site unit power, no optics.
• Operation: butter smooth, thanks to Ebony Black laminate and real Teflon pads.

Here is another view:

Yes, that is a little residual snow on the ground, and yes, I am standing there in a thin tee shirt. The shirt is special though: it is a one-of-a-kind air brush rendering of the top of Kitt Peak which Kathy purchased when she was visiting the tourist center atop Kitt Peak last summer.

My primary design and hints references are:

• Flexure of a Serrurier Truss, Roy Diffrient, page 91, February 1994, Sky and Telescope.
• The Modern Dobsonian, Tom Clark, Tectron Telescopes, 1992
• Collimating Your Telescope, page 259-263, March 1988, Sky and Telescope.
• Perspectives on Collimations, Vic Menard, Tectron Telescopes, 1987
• Newtonian Notes, Peter Francis, Kenneth Novak and Co, 1976

Here is a gzipped tar file of some drawings of the telescope tube and rocker box in KeyCAD .kcf format, and a spreadsheet of the basic optical formulas which is very handy for the design phase. The speadsheet I used is the free UNIX ss program.

My home observatory story.
My resume.
Xephem, my astronomy program for X Windows.
email: ecdowney@ClearSkyInstitute.com