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Modifying the Meade 8 inch Dobsonian
For Christmas, 2001, I bought an eight inch Meade dobsonian. My research indicated that several other scopes were mechanically superior to the Meade, but Meade was well known for the fine optics in their dobs. To me, as long as the optics were good, mechanicals can be fixed. So I bought it with the understanding that I would have to make changes to the scope. That was going to be part of the fun. With many scopes, there is just nothing that needs improving, so you don't get a real hands on feeling about your telescope. With the Meade, there are so many things that need to be changed that I had absolutely no qualms about drilling new holes in the tube to try something. I don't think I would feel that way about the Orion dobsonians for instance, they are just too beautiful. I have a real feeling of ownership about my Meade. I have tried some things that didn't work out, so I just put plugs in the extra holes. Actually when I got the scope, it already had some extra holes with plugs where Meade had tried to put the altitude bearings in the wrong place! I figure that if they can do it, so can I!!!
The first change I made was somewhat major. Meade designed its mirror cell for the dobsonian with a 7 inch diameter half inch thick steel plate placed right behind the mirror. Now this makes for a very low center of gravity and a nice compact base, but it also makes for a scope that will never cool down. The weight had to go. But when the weight was removed, the center of gravity moved nearly 4 inches up the scope, so the base had to be rebuilt. A trip to Home Depot for a 48 inch melamine particleboard shelf provided the necessary material. The melamine shelf appears to be exactly the same material as the existing base. I just cut a four inch hole in the exact center of the shelf and then cut the shelf in half (through the hole) and I had taller uprights to replace the now too short original uprights for the base.
I liked the idea of the spring arrangement from the Orion scopes, so I designed my own. I replaced the bolts holding the altitude bearings with longer bolts and added another pair of lock nuts, with a very short piece of threaded copper tubing between the two lock nuts, a couple of springs threaded onto the copper tubing, and a pair of turnbuckles. The tricky part was fashioning a four inch diameter padded washer for the inside of the tube to protect the tube and secure the bearings. By the way, I think that the larger curved washer is a good idea for anyone with a commercial dob using a sonotube. A padded round aluminum blank cover for an electrical box worked beautifully (Red Dot part number RSSB S341E from Home Depot). Just drill a hole in the center, bend it to the shape of the inside of the tube and paint it flat black. While I was at it, I superglued the holes in the tube to make them stronger. A very good idea for anyone with a sonotube dob, but not mine. I got if off of the web. I just don't remember where or I would give credit to the fine gent who came up with it.
In response to the recent article in Sky and Telescope, I got out my drill and cut a couple of one and a half inch holes in my tube at just above mirror height. I added a small fan to blow air across the face of the mirror. The combination of removing the steel plate and adding the fan has improved my views about 100%. Darn, but this is fun!!!! It is cool to see a positive response to your efforts. I installed the fan on a small block of wood that is angled slightly downward so the fan will blow directly at the center of the mirror. I am holding the block of wood in place with a chain of rubber bands, but I am working on a better arrangement. I am currently using a 9 volt battery to power the fan, but am looking for a better alternative for that too.