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8-Inch f/5.5 Split-Ring Netwonian

Built by Shane LaPierre of Connecticut   2000-Aug-29

Photo
8-Inch f/5.5 Split-Ring Netwonian
built by Shane LaPierre.
Shane's Scope

In 1998 I relocated from light-polluted Jacksonville, FL to the beautiful hills in NW Connecticut. I found plenty of good deep skies, and found myself using my 10" home-built dob a lot more often. I had a crave for a bigger scope, however, and so I planned for a new 20" which can be seen on my home-page. But I also wanted to have a telescope that could ride piggy-back on the 20" as well as be used solo. It turns out that I came across a piece of plate glass close to 8" in diameter, almost 3/4" thick, and slumped to a curve of 44" focal length. I decided to make a telescope using this plate glass, and so I fine ground, polished and figured the mirror utilizing foucault, ronchi & star tests to create a telescope that will leave any newcomer full of confidence. This was my first mirror, and it gives very good images. I have used it above 400X with good seeing on the planets, and I am thrilled with its performance.

I decided on a split-ring mount for the telescope. The reason is I have an interest in doing photography. I have nearly finished the Cookbook 245 CCD camera as of 8/2000 and I wanted a stable mounting to track on. The mounting is built with baltic birch. I built the bearings out of maple blocks with teflon inserts. The shafts are 1" aluminum. The optical tube is a truss tube. The upper cage is made of a couple of baltic birch rings, a focuser board and 1/2" aluminum struts. I used kydex as a light baffle. On the mirror end, I had to do a little design work. The entire optical tube can rotate inside of the hex structure. To faciliate this movement, the back of the optical tube pivots inside the hex structure with teflon vs. ebony star formica and a bolt to keep things concentric. I also added collimation bolts to the front of the mirror cell to allow collimation from the eyepiece. In practice all of this means that while sitting down, the user can point the scope, rotate the optical tube for convenient eyepiece location, and collimate without ever getting up. It sure beats standing on a ladder.

Besides riding in the split-ring mount, it can also be used on my 20". It's purpose is simply a giant-sized finder. It gives 2 1/3 degree FOV with a Pentax XL40mm lens, A 7MM exit pupil, and is perfect for just about any deep sky object.

I would like to commend the Springfield Telescope Makers for their commitment to fostering telescope making. I had my beginning as a 13 year old who had access only to books for information. I saw many pictures of Stellafane, and used many ideas from the old pictures. Now I visit in the summer, and have brought two new scopes in two years. I hope to bring many more in the future.

(See other photos of this scope on the 2000 StellafaneConvention Telescope Competition Pages)

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