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Hi Greg,
The advantages of the new configuration are several. First the whole thing is very much lighter. I was having serious problems manhandling the tube assembly of the old setup around as the bloody thing was very heavy. At 72 I don't do anything to overstress the body. Second, the whole thing breaks down into smaller pieces when necessary for fairly easy transport. It only takes about 10 minutes to take it appart and the same time to put it back together. Third, the addition of the equatorial platform for the base makes use of the scope much easier and more satisfying.
The tube structure is extremely ridgid and shows no signs of unwanted flexability. I made all the connecting supports of 1"X1" wood corner molding and made sure they were identical by using a drill jig. As a result, I don't bother to mark which piece goes where and no matter how I assemble it, the collimation is always close enough for use with no problems. Because the mirror positioning adjustments are close at hand, collimatin is easy when required right from the eyepiece so you can see what you are doing as you make adjustments. I have also put extra holes in the support pieces so that I can change the over all seperation of the of the base mirror tube assembly and the upper cage. This lets me move the focal plane further out to accomodate the use of a prime focus camera.
I don't remember exactly how the original was collimated, it's been a few years since the rebuild. I do remember that it was never really good and was always difficult to do.
The secondary is offset and the design of the spider permits very easy adjustment of the complete positioning of the secondary for all conditions.
The images are better now and I can really appreciate what a good mirror this is. Many of Coulters mirrors left a lot to be desired and I think this was one of the better ones.
All in all, I consider the rebuild to have been a success. All materiels were readily obtained, most from the local hardware/lumber yard here. The inner surface of both tube sections is covered with black felt from the local fabric shop and works very well. It also helps to prevent dewing of the mirror although I haven't understood why yet.
The tube material to use for the tube sections is readily obtainable "Sonotube" although I could have used the original Coulter tube and cut it down. I didn't think to do that until I had completed the rebuild or I would have.
The equatorial platform is of my own design and was fairly easy to make. There are no teflon pads or formica surfaces for them to run on. Instead I use a 12' lazy susan ball bearing assembly for the azimuth bearing and hardware store flange ball bearings for the elevation. These are very smooth and friction is controlled by very large flat washers between the upright supports and the tube assembly.
To finish, I'm happy with it and will use it until I get my 20" finished.
Jarvis Krumbein |
