The Planetary DOB The image at left shows my 6 inch f/10 planetary DOB. It was designed as a kit by Stargazer Steve, and was used to make the Mars drawings on the Mars Drawings page. I purchased my 6 inch f/10 DOB as a special design from Stargazer Steve Dodson. He has his own site at Stargazer Steve. If you don't know about Steve, he's a very accomplished telescope maker and educator making his home in Canada. He sells a range of reflecting telescopes of his own design packaged as kits. With Steve's kits, optics are delivered already finished, and many parts, including the mount elements, are pre-fabricated. So assembly is pretty easy, usually taking only a day or two.

I'd been corresponding for a time with Steve about whether his 6 inch f/8 DOB would make a good planetary telescope. After some back and forth email, Steve sent a response saying he knew what I wanted. A long focus Newtonian on a DOB mount, with each component designed to give the best planetary performance.

So he offered to make a 6 inch f/10 kit for me and quoted a price. The price was a bit more than his regular 6 inch, but seemed fair given the special effort he'd have to expend on the project. In retrospect, it was probably a bargain.

I agreed, and he delivered. The telescope arrived a few months later, well packed and already partially assembled. All I had to do was put together the mount.

Steve likes to make his DOBs with most of the telescope weight on the primary end. This makes for a very low profile and small footprint DOB base, as shown in the picture. On his regular DOB models, Steve does this with a specially designed mirror mount that has room behind the mirror for some counterweight material.

My scope is quite a bit bigger than the normal Steve 6 inch because of the performance I was seeking.

The tube is 6 feet long to accommodate the mirror focal length, and 9 inches in diameter to keep tube currents out of the optical path. The longer tube required a mirror design that would allow more counterweight to achieve Steve's signature low profile mount.

Steve accomplished this with a wooden ring at the bottom end of the telescope with 1 1/2 inch holes spaced around the ring. Counterweights are 1 1/2 inch bolts which can be mounted in the holes. I can use the number of bolts necessary to accommodate the amount of counterweight needed to balance the telescope.

In Search of Perfect Images The basic design elements that give great planetary performance are numerous. An oversized tube to keep air currents out of the optical path. A Pyrex primary to minimize cooling problems. A long focal length to give a flatter field, minimize alignment errors, give better power per eyepiece, and allow a smaller secondary. The reduced sized secondary is only about 16% the diameter of the primary, and gives negligible diffraction. The telescope also uses a curved secondary holder to eliminate spikes. The mount is made of heavy-duty birch plywood, with the sides of the DOB box being double layered.

On the base are 3 Teflon pads. Mounted to the under of the DOB box is a metal sheet that makes the bearing surface for the Teflon pads.

Heavy-Duty and Cleverly Designed The elevation bearings are two short lengths of 1/4 inch thick, 6 inch diameter aluminum pipe. Mounted to the sides of the telescope cradle, the aluminum pipes ride on Teflon bearings. The elevation bearing on the left side of the mount has a cleverly designed adjustable brake to allow for variation in eyepiece weight.

The Telescope in Use

The result? A smooth operating mount that is very steady, and a telescope that gives superb planetary images. There has been little for me to do but enjoy the ride.

After using the telescope a lot, I did find that moving the telescope around did present a problem, or at least an inconvenience. I had to lift the bulky 6 foot tube from the base, then move the base to a desired spot, then re-affix the tube to the mount.

I kept bumping one of the elevation Teflon pads and working it loose when I removed and replaced the telescope tube. I needed a way to move the telescope without disassembling it.

First Refinement, Wheels This prompted my first refinement. I mounted a pair of metal brackets to the base to allow me to slip an axle with wheels into position for moving the assembled apparatus. I can easily remove the axle and wheels when the telescope is where I want it. I just slightly tip the base and the wheels drop out of slots that hold them in place.

Second Refinement -- Mirror Fan I eventually added a second refinement: a computer muffin fan in the bottom end of the telescope. The cooling fan is mounted to a circle of 1/8 inch hardboard with a hole cut the size of the fan. Three elastic straps (ponytail bands) suspend the fan in place, and absorb any vibrations generated by the fan (the 3 red arrows). With the elastic bands, the muffin fan doesn't cause any discernible vibration, aids in cooling down the mirror and optical path, and breaks up the turbulent convection layer that tends to sit over the primary's reflective surface. It really lets the telescope deliver refractor-like images.

Recommendations

Would I recommend a Stargazer Steve kit to a prospective buyer? Yes, with no reservations. Steve's telescopes are cleverly designed, and built heavy duty with quality parts. He is also very helpful if you need any assistance after purchase.

I've used my DOB for quite awhile now, and find that the design makes the telescope easy to maneuver. The telescope is also very steady, a great accomplishment with such a large design.

If you're interested in a DOB, the astro-customized search engine at right searches through a number of popular telescope outlets.

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