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Building My 8" Newtonian Reflector

"And finally, there is understandably the stimulus of being able to unlock the mysteries of the heavens by a tool fashioned by one's own hand".
Russell W. Porter, March 1923 - founder of Stellafane
 

In the Beginning ...

... there was only a dream, and the dream was mine, and the dream was about having a large telescope...

It all started when my friends living a couple of blocks away (in Istanbul, Turkey) had considered building a telescope of their own. Several times a month, we were getting together to discuss different techniques of telescope making, its difficulties, obstacles we can encounter and possible solutions we could think of. Finally the decision was made. Due to lack of necessary equipment, knowledge and material (carborondum, pitch lap, etc.) we eliminated the option to make mirrors by ourselves. Then we moved on with the second option: buying out ready-made commercial mirrors from abroad.

Whilst my friends got a 10" parabolic mirror from Broadhurst, Clarkson and Fuller in London, UK; thanks to the financial help of my father A. Fuat Menali, I ordered an 8" parabolic mirror and a corresponding diagonal from Meade Instruments Corp. in California together with a 9mm Orthoscopic eyepiece and a 3X barlow lens in March 1984.

As soon as the small package arrived via Switzerland (to avoid exorbitant Turkish customs duties) in May 1984, I started working on the plans of my future dream telescope. I carefully measured the focal length and draw detailed schematics on millimetric paper. I had found a very useful resource at the library of the Bogazici University where I was attending to the Business School: "Telescopes: How to Make Them and Use Them”, Vol 4, Sky and Telescope The Macmillan Library of Astronomy, published in 1966. Also, I happened to have a xerox copy of the first French edition of Jean Texeraux's "How to Make a Telescope". These two books helped me to understand basics of telescope design and construction. Additionally I went through hundreds of pages in both Sky and Telescope and Astronomy magazines at the university library to check almost every article published on telescope making (I subscribed to both in 1985, after I jumped into the ATM effort).

The people who know me closely are aware that before embarking on any challenging project in my life, I like to analyze it in depth and plan thoroughly ahead. In a couple of weeks my telescope was ready, of course only on the drawing paper! I even constructed a small scale replica from cardboard. Now was the time to tackle the real task: building an 8" reflecting newtonian telescope! With a very important problem at hand ...

 

The Problem

At the very start of my endeavor I had a very challenging problem: in Turkey none of the telescope accessories was readily available in the market. Not only it was due to lack of even a single astronomical instrument component manufacturer available in the country (things got started improving in April 2006 after my friends and I established ATM Turk, a discussion list over the internet for Turkish speaking ATMs), nor there was any company importing them as well (please check out our Turkish Astronomical Links page for current vendors in Turkey). So what did I have to do?

 

The Solution

I had to improvise and find a way out how to build each one of these components. As I did not have any tools nor any experience in using such tools, I had to seek for professional help. As a result, I decided to go to different workshops where I can ask for a specific component to be built. So I did ...

 

The Tube

I had decided that I should use a lightweight material for the tube so that it could be easily handled and transported. Among the options I considered were either building a tube from cardboard ("Sonotube" or similar) or using thin aluminum pipe (similar to my 50mm refractor) of large aperture (9 inch or so). However I gave up the idea of using these materials as they were either not strong enough or too heavy. Then it came to my mind that I was very well aware of such a material which was really tough, yet considerably lighter than any other that might be used in telescope making: fiberglass!

The only places where I could find somebody to help me to build one were either containment tank (for fluids) constructors or auto body workshops. I chose the latter as an industrial park full of auto body shops was conveniently located near my neighborhood. The rest was relatively easy. I chose one such workshop and explained the guy, who never knew what a telescope was in his entire life, what purpose I would use the tube for. To my utter astonishment, he came up with a very clever idea of using a steel mold which had the shape of half a cylinder. He cast the first half of the tube in the cylinder, then the second half was cast and both halves glued together with sheets of fiberglass.  Update as of April 2006:   I went to the shop of the same guy in April 2006 when my wife Gamze and I were in Turkey to watch the total solar eclipse from near Side on the Mediaterranean coast. He helped me to install on the tube a 2" second-hand focuser that I had bought at NEAF a year earlier. I also remembered what his name was:  Ahmet Erturk. He instantly recognized me, and the tube he put together, more than 20 years ago!

In a couple of days my telescope tube was ready! And it was weighting less than 6 pounds so that I was carrying it with just one hand! Wasn't that unbelievable? I had started building my dream scope at last!

In order to reduce internal reflections I used flat black paint for the interior of the tube. Although I worked inside out applying the paint with a brush, you should have seen me after I had finished the work! I can just say that I could not wear the same T-shirt again! For the exterior color I chose glossy white to be sprayed at an auto body shop. I preferred white color just for aesthetic reasons even though it is not recommended as it takes longer for a white tube to cool down to ambient temperature. A minor nuisance for me! I wanted to see stars, not to build a masterpiece.

I had to find another workshop to have the mirror cell built from iron. The cell consisted of two concentric rings (1). The outer ring of the cell fitted outside of the tube which it was attached to with bolts and nuts at three equidistant points. The primary mirror was placed on the ring inside and was supported by a layer of ½ inch thick rubber bands underneath and all around it. The collimation of the primary mirror is done through three bolts-nuts combined with springs which were placed at the rear of the rings (2). It's sure that rubber bands applied some pressure to the mirror, but the resulting astigmatism was not too much noticeable. Oh well, who cares?

For the diagonal holder, I went to a carpenter who carved me one from wood with his lathe. It was of cylindrical shape with a short rod at one end (to be attached to the support wanes), and the other end was cut at a 45 degree angle to accommodate the secondary mirror. I glued the diagonal mirror to the holder. To make sure that it won't get loose, I also fastened two thin steel plates like clips to hold it in place. The spider had been built again by the same workshop where the primary mirror cell had been cast. It consisted of a small round iron plate in the center, attached to an iron ring via two thin iron rods. Even though I tried to have curved support wanes (to minimize spike effect) by using thin steel rods after a Sky and Telescope article (May 1985, page 459), the steel rods did not stay as rigid. As a result, I adopted a two-waned spider, instead of a regular one with three or four. The small iron plate in the center was threaded with three small holes through which small bolts with springs were attaching it to the diagonal holder, also allowing the collimation of the diagonal mirror.

The first focuser I had was made of two thin iron pipes used like a helical focuser. However, it was not really efficient because of their friction problem. Consequently I had to look for another material easier to work with. I ended up in going to a brass workshop manufacturing boat propellers. In less than a week I was mounting a simple but very user-friendly brass focusing mount to my tube. It consisted of two brass tubes gliding within each other (3). The outer tube had a round base which I had fastened to a square wooden plate with four screws.

I use two finderscopes on my telescope: 8x30 monocular attached directly to the tube in front and a 20x60 monocular mounted on the telescope box. In the pictures below (except the ones for the setup process) and on the Our Observing Instruments page you can see my original 5x40 homemade finderscope. Later on I replaced it with the current 8x30 monocular seen in the setup pictures below.

To my dismay, the tube of the telescope had been completed long after Halley's Comet disappeared in northern skies. Its construction took longer than I had originally planned. For almost two years I used the tube as it was, without any mount. I was putting the end of the tube on the ground and just trying to hold it steady with my arms whilst looking through the eyepiece. Although I had bought my second eyepiece, a 20mm Erfle, from Broadhurst Clarkson and Fuller in London in 1986, the field of view was still narrow to do serious observing. I remember observing the opposition of Mars and making out some surface features in May 1988. In June 1988 it was time to go to Paris, France to start my career in banking. With my heart broken, I left my tube-scope back home. It wasn't after my return to Turkey in fall of 1989 that I would resume where I left in building my telescope ...

  

The Fork

Since I have first seen Edmund Scientific's fork-mounted reflectors on their catalogs in early 1980's, I fell in love with the idea of using a fork mount in my future telescope. The only pitfall was that I had no clue on how to build one. Until I came upon another book about telescope making. The year was 1988 and I was living and working in Paris, France. The book was titled "Mon Telescope, Mon Observatoire, Pourquoi Pas?" (My Telescope, My Observatory, Why Not?; 2nd edition, 1985). It was written by the prolific astronomy popularizer, writer and telescope maker, Pierre Bourge, together with Jean-Marc Becker, an amateur astronomer as its co-author (you can see a Bourge-type telescope described in the book at this French site).

That book gave me the exact idea on how to build the fork mount I wanted so desperately. Actually I also met two young optical technicians working at the REOSC Optique company (manufacturer of optical systems for satellites, polisher of ESO's VLT mirrors), also amateur astronomers, during a visit organized by the Association Francaise d'Astronomie to Nancay Radio Astronomy Observatory. One of them, Jean-Marie, had already built an exact textbook copy of Bourge-type fork-mounted 8" newtonian (can you believe my luck?). Moreover, we had at least two observing runs with his telescope in Frettes, a small town near Dijon, east of France, close to the Alps. So I had enough time to examine it closely and take as many pictures as I could. I had already decided how my future telescope would look like.

Another bonus feature of Jean-Marie’s telescope was that he was repositioning the eyepiece to a convenient location by rotating the tube. He had built a box similar to a dobsonian’s rocker box and placed the tube inside. He used some sort of clamp system which was loosened to turn the tube within the box to have the eyepiece easily accessible wherever the telescope is pointed to. This way the balancing of the tube was also easily done, by moving it back and forth. I had a similar box and clamp system built on my telescope (4).  As a result looking through my scope is really convenient and easy.

The lower part of the tube-rocker box is strenghtened by triangular MDF supports diagonally placed in each corner. The surfaces of these supports, which are in contact with the tube, are covered with used black velvet strips to prevent the tube from scratches.

For the fork arms I used 1-inch thick medium density fiber (MDF) stock which is considerably light, strong and easy to work with. As you can see in the pictures below, I first had to put a frame for the arms so that they form a U shape (or two L’s placed face to face). The bottom of the U consists of two levels of MDF separated 5", to make the arms stronger. Just underneath of the upper level, two sides of the U arms were connected together by two long bolts and hardly tightened by nuts, in order to strongly keep the arms together (5). I fastened used ball bearing covers (bought from an auto junkyard) to either side of the tube box as side bearings. They formed the altitude axis. The upper ends of the fork arms were finished in 4" wide U-shaped openings. Bearing covers sit on these openings squarely. At the start I was thinking that I would need to place teflon pads to provide friction, but steel bearing covers' friction against MDF was enough to keep the whole box-tube combination in balance. So, in a way, my telescope’s basics are those of a dobsonian after all.

To finish the fork arms I covered the framework with plywood and applied brown furniture paint all around. I had a 2-inch hole drilled (6) in the middle of the two bottom levels of the U, to place a steel shaft (7) for Right Ascension later on. And this story takes us to the next phase in the construction of my telescope ...

 

The Mount

By the time the tube and the fork were completed, another important part of the telescope was still not around: the mount. From the winter of 1989 until the end of summer in 1990 (mostly during 1990 summer months) I used my reflector as a dobsonian. Having not yet decided on what the mount would look like, I was just placing the tube into its craddle and putting the fork arm on a cardboard on the ground. Then I was moving the fork in azimuth. Although it was not as smooth as a real dobsonian, I was happy enough to use it in observing several objects, including comet Levy (C/1990 K1).

However I needed an ultimate solution to place my fork mounted tube onto a real mount, in order to start making some serious observing.

As you know (from my story above) I consider myself as a lucky guy (in terms of telescope making and also marriage). The AAVSO was organizing its first European meeting in Brussels, Belgium in July 1990. I had to go there! So I did. The first day, during one of the coffee breaks I was meeting with several people I only knew by their pictures and their names (such as Gerry Dyck of Assonet, MA and Rev. Robert Evans of Australia). Then, there was this display area where people posted their papers, pictures and observation results. I remember that while wandering in front of the displays I stopped in front of one booth, prepared by Belgian amateurs, showing several pictures of homemade telescopes. And there it was, standing amidst other pictures, a white colored homemade newtonian (yes you guessed it right, an 8" beauty) standing on a triangular box-shaped mount, the fork arms attached to the mount with a pipe which was supporting the R.A. axis. Fortunately I did not scream "Eureka!", however I took several close-up pictures, of that one and others.

Upon my return to Istanbul from that meeting, I was working like crazy on the mount. To the contrary of the Belgian mount I pictured, I wanted my mount to be fully portable. So I set aside the idea of having a box-shaped mount and chose a modular approach. Eventually, I ended up with using two MDF boards, attached to each other with a long furniture hinge (8), so that I can fold the boards down for easy carrying. I also used two aluminum pipes (9) to elevate the upper board on the ground one with an angle of 45 degrees (a rough polar alignment). Although I was going to install just small plastic feet on the underside of the ground board first, my grandmother who was visiting my parents gave me another idea: “why don’t you use wheels to roll it around?” she asked (now I call this a family of astronomers, yeah). Thus I placed four small rubber wheels at each corner. In order to stabilize the ground board during observing sessions I had five holes drilled, at each corner and in the middle, glued large nuts in the holes and put large bolts (10) fitting through them. When I am carrying the board to the observing site, I roll it around easily. Then I stabilize it by turning the bolts in and raising the board over the ground, and thus polar aligning the scope.

I used a 15" long steel pipe for the R.A. shaft. It goes through the holes on two bottom layers of the fork arm and is screwed to the upper part through a plate (6). In order to attach the shaft to the elevated board and turn the fork in R.A. axis I glided it through two used auto ball bearings (11). Bearings themselves were attached to the board by reversed-U-shaped clamps made of iron. To increase the friction and have the fork turn tighter I used a reversed wooden U-clamp in the middle of the shaft (12).

For now the mount is an equatorial without the tracking capability. However my plans, adopted from the French book, are ready to include a star-tracking device. I think it will take another couple of years before I complete it!

 


Numbers correspond to sections explained in the text.

 

... In the End

The construction of the my entirely-home-built-telescope-except-the-optics had been completed in 1990. Since then it helped me and others to see the universe with another perspective. From light polluted skies of Istanbul I could easily reach magnitude 13 and from my parents’ summer house on the southern Marmara Sea coastline I saw stars down to 14th magnitude. Unfortunately, I am away from my beloved telescope again since I could not take it with me when we moved to Boston in 1997. I am looking forward to uniting with it in a short while and continue stargazing and observing the heavens with it. As Emile Schweitzer of AFOEV had put it in one of his letters once, “astronomy is a field of research requiring lots of patience”. I am patient and will be waiting to look through my 8” one night again. In the meantime, I am admiring the skies through Mary Ann, our computerized 8" SCT.

Update as of September 2007

Finally! My beloved 8" scope and I are together again :o)! I have it shipped from Istanbul to Boston, with the rest of our fine furniture. I look forward to the night I will be observing through it again.

Update as of August 2009

Another one of my dreams come true, at last! This year I finally brought my beloved 8" scope to the Stellafane convention and displayed it on top of the Breezy Hill, near the Pink Clubhouse and the Porter Turret telescope :o)! Thanks to the awesome weather, I observed with my scope both in front of the Porter Turret telescope and the McGregor Observatory on three consecutive nights, in August 13th, 14th and 15th! I also got the "displayed at Stellafane" sticker that I am now proudly carrying on my scope.

Epilogue

As someone mentioned it correctly during the Friday tent talks at Stellafane in 1998 (our first convention): "telescope making is an art of inspiration". There is nothing wrong if you start looking at findings and ideas of other amateur telescope makers to come up with solutions of your own when you build your telescope. In turn, other amateurs will copy your ideas and your scope's features and again those of many others to build their telescopes. And this cycle will go on, forever ... Now it is your turn to grasp some ideas from my homemade newtonian to build your own. Good luck in your endeavor!

 

"It is not ... unsportsmanlike to study closely the details of telescopes made by others and to 'lift' this or that feature from them, provided one improves these features."
Albert G. Ingalls

 

Setting It Up

Below I post several pictures to show you how the scope's setup is done before an observing session.


Left: Getting the components together; the base, the tube, the fork.
Right: Preparing the base; I am putting aluminum pipes in place to raise the polar board.


Left: Fastening the wooden "U" clamp onto the board to keep R.A. steel shaft tightly in place.
Right: Checking the collimation.


Balancing the tube within the "rocker" box.

 

"If there were a million amateur astronomers with telescopes, and they were willing to let a few thousand people each look through their telescopes, there would be a chance for the people in the world who wanted to see to see."
John Dobson

AMATEUR TELESCOPE MAKING LINKS

Amateur Telescope Making WebRing, by Yahoo.
The Annual Telescope Optics Workshop, Western Washington University.
ATM FAQ by the Atlanta Astronomy Club.
ATM Journal
ATM Links, by Willie Koorts.
Astronomy Daily, now includes the former "ATM Page".
ATM's Resource List by Bob Lombardi.
Dan Cassaro's ATM Page
Group 70, a group of amateurs to built the largest telecope in the world.
How to Choose a Quality Telescope for Under $500.00, by David Lent (the original link is dead due to re-construction).
Krajci's Tension Spring Dobsonian
Lin Robertson's ATM Home Page
Mel Bartels' Home Page
Mel Bartels' Computerized Dobsonian
Ray Cash's ATM Website
RTMC Astronomy Expo, formerly Riverside Telescope Makers Conference
San Fransisco Sidewalk Astronomers
S*T*A*R Astronomy ATM Web Ring
Telescopes and Telescope Making, by Mel Bartels.
Telescope Making Web Ring, where this page is also listed.

SELECTED ASTRONOMICAL EQUIPMENT REVIEW LINKS 

Astronomical Equipment Reviews
Astronomical Observing with Telescopes
Chip Baines' Product Descriptions and Reviews
Cloudy Nights Telescope and Accessories Reviews, by M8 Inc.
Darwin Bagley's Reviews
Excelsis Ratings, ratings for many instruments including astronomy equipment. 
Joe Bergeron's Equipment Reviews
NOVAC Telescope Reviews
Rick's Low to Mid Range Telescope Review Web Site
Rod Mollise's SCT-User Mailing List Home Page
SCT Tips, by Ted Kurkowski
SkyNews Magazine Telescope Reviews
Sky & Telescope Test Reports, pay per report.
Telescope Owner Resources, by The Open Directory Project.
Telescope Reviews by Jason Blaschka  
The Telescope Review Web Site, by Ed Ting of New Hampshire. A short note: when I met Ed during my wife's and mine first Stellafane convention in 1998, I did not know who he was. He gave me his astronomy business card when we were observing in complete darkness. Very much later, when I checked the card and read his name, I said to myself: "Darn! I should have talked to him more to ask his advice on many things".
Todd Gross' Equipment Reviews

 

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