A Twenty-Four Year Telescope Odyssey

My love of telescopes started when I first looked through one at the age of twelve. My neighbor was out in his front yard with a 60-millimeter Tasco Telescope that he had just purchased. He showed me the moon and I was forever changed.

In high school I learned how to make a telescope from reading a book by Allen R. Thompson. I got my supplies from Cave Optical in Long Beach, Calif. I successfully ground, polished, and figured a 6-inch f/8 mirror. After that I made a 6-inch f/4, a 4-inch f/10 and an 8-inch f/12 Dall Kirkham Cassegrain. Like most people, I was always disappointed when looking at faint objects. I needed to go bigger.

Back in the 1980’s and 90’s amateur telescope making went through a big transition. The Dobsonian telescope was born. Amateurs were now making mirrors up to 16 inches in diameter and they were transportable. During this time the Coulter Optical Co. started selling a there commercial version of Dobsonian telescopes. In 1990 I decided to purchase their 13.1-inch f/4.5 “Odyssey”.

1990 13.1" Coulter Odyssey W/new 2" focuser and Telrad setup

1990 13.1″ Coulter Odyssey with new 2″ focuser, Telrad setup, extra handles, and wheels for easy transporting to storage area.

This scope sold for $600.00 where a traditional telescope of this size would have cost $2,500.00 and have weighed about 350 pounds. This scope could fit in the back of my car and only weighed 120 pounds (60 for the tube and 60 for the stand). The Odyssey had a good reputation but needed a lot of tweaking to make it a good scope. The original focuser was very simple (not good). the spider and secondary mirror were not adjustable. Hot air was trapped inside the tube and it took forever for the mirror to reach the outside temperature. The best thing about the scope was its price and its light gathering power. Low power was great but it never gave good views of the planets. Something was wrong. Coulter always sent his scopes with a Ronchi Band Tester to show the buyer that the mirror was at least ¼ wave corrected. When focused on a star the bands should appear as straight lines across the mirror. When I looked at mine they were pretty straight across the mirror but the edge was slightly curved showing a turned down edge. I thought the mirror was ok so I thought that the scope had to be misaligned and not collimated correctly. I spent many weekends trying to adjust the alignment and collimation. Sometimes the images were better but I was never satisfied.

In 2009, I decided to go from a tube design to the open truss design. This design enables the scope to be broken down into small pieces and is lighter weight. It also lets air to reach the mirror allowing it to reach the ambient temperature faster.

I purchased a kit for Dob Stuff.com. I figured that this would be the easiest and fastest way for me the get the scope updated and useable. The kit was great. All of the parts were made of high quality plywood and they were all precision cut. All I had to do was to finish sand them and assemble there. The scope worked much better. High power was still a problem. The planets would not come into sharp focus. I again spent a lot of time making sure that everything was perfectly aligned. The image kept getting better but I still was not satisfied.

Dob Kit assembled from Dob Stuff.Com

Dob Kit assembled from Dob Stuff.Com

March of 2014 I decided to send my mirror out to be refigured. I contacted Steve Swayze of Swayze Optical Co. and asked him if he could refigure my mirror. He wanted to know what type of glass the mirror was made of. In the early days, Coulter used Pyrex glass that was just over 1 inch thick. In the later years, Coulter changed to plate glass, which was about ¾ inch thick. If I had a Pyrex mirror Steve was pretty confident that he could get a good correction on the mirror. If it was plate glass he could correct it but could not guarantee how good he could get it. Fortunately I had a Pyrex mirror. I asked Steve if he could take some pictures, before and after, of my mirror under test. He said that it is very hard to do but he would try.

When Steve received the mirror he told me that the mirror wasn’t too bad. It did have a very slight turned edge and a slight hump in the middle. I told him to go ahead and correct the mirror because I was not happy with its performance.

Below are two pictures that tell the story of the mirrors correction. The defects are very subtle but the effect on the image is great

Slide1Before

Slide2After

On May 28,2014, I took the scope with its newly refigured mirror up to Big Meadows for some clear, cold (38 deg.) dark skies. The Sky was stunning and so were the images in the telescope. The first object I aimed the scope to was Saturn. It was very clearer with my 8mm eyepiece and Barlow at 370X. The focus point was very exact. Next I aimed the scope at M51 (The Whirlpool Galaxy). Wow, It came in very sharp I could see the spirals in the arms and the bridge between the two galaxies. Next I did a “star test” It was perfect. The Diffraction rings were textbook.  I wanted to check out the optical quality using the Coulter Ronchi Tester. Again, the bands were perfect. No sign of any imperfections could be detected.

Over the years I replaced everything on this telescope; the focuser, the spider (3 times), the diagonal mirror holder (3 times), the red tube, the rocker box and the bearings. I added digital setting circles and a Telrad finder. The only things that are original are the 13.1-inch mirror and the 3.1-inch secondary mirror. After 24 years trying to fix this scope, I finally achieved it. This Odyssey is over. The only week link in the optical system left is my eye.

FinishedCoulterCroped

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Author


Greg Eckes

President

I am a retired music teacher. I make custom violins and violas. I play violin in the Tulare County Symphony and fiddle in the Tule River Bluegrass Band. I like camping and astronomy.

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