But My Telescope CAME With Rings!!!

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Emil Stephens
5 years ago
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1 But My Telescope CAME With Rings!!! By Clay Kessler Telescope Support Systems Most of the commercial telescopes that are purchased come with either rings or a mounted dovetail plate of one size or another. If you are a visual observer please be assured that what your scope is equipped with will probably be adequate for your use. As imagers we all know that flexure can be introduced to a system from a number of sources. Many of the telescopes sold today incorporate rings or a dovetail system into the telescope tube usually with screws that are too small. Most of these situations can be improved for imaging systems. Let s look at some examples of imaging mountings and discuss how they can be improved for our purposes. As is happens, I picked up a used 10 inch Imaging Newtonian just a week ago. (I could not pass it up but to be fair I did not try very hard) You should realize that I think this scope represents a terrific value at it s full retail price. The manufacturer has incorporated a wealth of features to make this a good imaging system. I think, with a little effort it can be a great imaging system! I am currently climbing the learning curve with a cooled monochrome camera and I am using an Explore Scientific ED80 Triplet. I plan on using this setup for at least another year or more depending on clear skies. The 10 inch will be the next step in focal length for the monochrome camera so I have some time to fiddle with it. (please understand I like to fiddle so this is an added benefit for me) This telescope has an excellent reputation for imaging and the fellow I purchased it from only sold it because it was pretty heavy for his mount it is a heavy bugger! The following is not to cast aspersions on the telescope. I think it is a super buy for the money that they charge. Used it was irresistible to me, not that I tried very hard. These telescopes are designed to provide a LOT of telescope for the money and they deliver. My purpose is to point out why a serious imager may want to invest some more into the scope to take it to the next level and make it much easier to use.

2 The first thing I noticed is, of course, the rings. These rings are typical of the rings on the value priced telescopes. The manufacturer has to make the scope to a price point that will be attractive to users. Economizing on the rings helps to hold that very attractive price. The rings are cast aluminum (or an aluminum like material) and have an attachment boss at the top and the bottom. A 20mm (.8 ) diameter hand knob is provided for fastening the ring halves together. The rings themselves are relatively wide at 40mm (1.575 ) but they are only about 6mm (1/4 ) thick. The felt in the rings has taken a set and is uneven but looks to have been about 5mm thick. At the top and bottom of the rings is a boss for attaching a dovetail plate. Each boss has a single ¼-20 tapped hole and is 1 wide X 1 ¾ long. The rings, including the top surface of the bosses, is painted with a heavy coat of hammer texture paint.

The felt in the rings has varying thickness now because it has taken a set and conformed to the shape of the seamed steel tube (not round). This telescope weighs 30 lbs!

3 Now what I see as issues: The rings are quite wide but being only ¼ thick they are not at all stiff. I can fasten the empty ring halves together tightly with the hand knob and visibly flex them with my hands. The thick felt means the felt can take a set and this leads to loose rings. The felt in the rings has varying thickness now because it has taken a set and conformed to the shape of the seamed steel tube (not round). This telescope weighs 30 lbs! I have a hard time trusting this size telescope to two 1/4 screws. The surface area of the boss is not only painted with irregular texture paint, it is very small. Using a D style plate the rings can rock against the plate as the telescope tracks a major source of flexure. In my experience I feel everything about these rings - small bosses, single screw attachment, hinged design, small hand knob, thin cross section and thick felt is a source of flexure to be traced down and eliminated.

Now you all know we here at Telescope Support Systems make rings. It should be no surprise that I am going to recommend replacing these rings to eliminate all of these flexure sources.

4 Now you all know we here at Telescope Support Systems make rings. It should be no surprise that I am going to recommend replacing these rings to eliminate all of these flexure sources. Our typical large OTA rings are made quite differently. We machine our rings from a solid billet of 6061-T6 aluminum. By machining the rings instead of casting we can use the opportunity to design strength and stiffness into the ring structure and pockets to reduce weight. Our rings for this size telescope are ¾ wide (rings for anything larger than a 10 scope go to 1 wide). We supply a top and bottom boss on each ring. The bosses are ¾ x 4. The 4 width matches a width of a D style dovetail plate. The bosses are machined flat and the rings are anodized to keep uneven paint away from attachment points. The bosses incorporate four (4) ¼-20 tapped holes to securely attach to the dovetail plate. This means the scope is attached with eight (8) ¼-20 screws! Our rings do not use hinges. The top half and the bottom half bolt together with 5/16-18 screws. The rings use 1/16 thick felt. The size of the rings is designed so that when the rings are bolted together the felt will crush 50%. This lets us bolt the rings until the top and bottom are a solid single unit and still float the tightly held tube in the center. Out of round steel tube no problem! It will be round when the bolts are tightened.

The thick walls of our rings, in combination with the solid hinge-less design, mean our ring system becomes a solid system with outside forces transferring through the rings and not through the

5 As you can see, the surface area of our ring boss is much larger and stretched the width of a D style plate as well as being machined smooth. This will remove a huge amount of potential flexure from this telescope. The relative thickness of the ring walls and the felt can be seen in this picture. The thick walls of our rings, in combination with the solid hinge-less design, mean our ring system becomes a solid system with outside forces transferring through the rings and not through the telescope tube. The tube is isolated from these forces unlike with hinged rings. Oh but how much weight have I added to the system with my new massive rings????? How about 6 ounces!! The stock rings weigh 1lb 9 oz. My new rings weigh 1 lb 12 oz. How can that be? When we design rings we remove weight where it is not needed and leave it where it is required for strength. I could remove more weight

6 without compromising strength if I had pierced the rings instead of cutting pockets but this is an added cost option and I do not carry those in stock. One other thing that I will do when I set this system up is to set the rings at a wide stance on the telescope tube. By using a 20 inch or so dovetail plate on the top and bottom of the rings I will be able to add stiffness between the focuser and rear cell of the telescope always looking to take out opportunities for flexure! I have lots to do to this system before it is ready to go on my mount. I suspect I will write further articles as I work on optimizing the setup to work at it s best for me. I am really looking forward to imaging with it! CWK

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