Birchardville Observatory
Site Always Under Development
This telescope is a 10" diameter Newtonian reflecting telescope using a Dobsonian mount. John Dobson's mount design has a low center of gravity and large bearing surfaces, so it is quite stable.

Although I don't have a picture of the scope broken down here, the diagonal cage fits into the mirror box so that it is quite compact when transporting the scope. This was another idea from Tom Clark.

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The focal length of this telescope is 1016 millimeters, giving a focal ratio of F4.0. This is considered short and fast -- relatively low magnification and wider field of view are a couple of its features.

10 inch F4 Reflecting Telescope

Standing on its feet, the telescope is less than four feet tall. No ladder or stool is needed to see through the eyepiece unless you are the size some of my grandchildren were when the scope was new, years ago.

Tom Clark recommended use of lightweight plastic sheet for the sides of the diagonal cage. I had some thin aluminum sheet available so I used it instead.

I used a hole saw and then a small roundover bit in my router to make the supports. I didn't save a lot of weight, but here in the cage, weight saving is helpful and it looks neat, too.

Diagonal Cage

I found 0.5 inch diameter aluminum tubing in 6 foot lengths at a store specializing in supplies for Amateur Radio antenna builders, Texas Towers of Plano Texas..

Eight truss tubes each just under two feet in length nicely used three 6-foot pieces of tubing.

The clamp blocks were made of maple blocks I laminated to get the size needed for the corners of the mirror box, and simpler clamps on the bottom of the diagonal cage.

Truss Tubes

When I built the scope some years ago, Jared was four years old. You can see that you don't need a lot of height to see through the eyepiece. The diagonal cage has the focuser mounted at the 45 degree point as it gives an easier viewing position as the elevation angle is reduced.

Dob with 4-year-old Jared

The short spiral threaded focuser is very light weight and does not intrude into the light path. Similarly, I chose a spider which had three legs as an option. I only tried the four-leg option once, and saw no benefit to it. Reducing the number of legs in the light path should reduce the diffraction spikes in images of bright objects.

Inside the Diagonal Cage

10 Inch F/4 Dobsonian Telescope

Features and Specifications

This telescope was homebuilt from some (key) commercial components, generally following the principles of Dave Kreige (of Obsession Telescopes) and many others.

The objective mirror was purchased from Discovery Telescopes in Southern California. Other key components included a cast aluminum mirror cell from .............. in Canada, focuser from Gary ...... in Canada, secondary (diagonal) mirror from ........... and the diagonal holder from ...............

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Contact Info:
Name:Dan Janda