The journey to building my first telescope by Michael Moller - ScopeX

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The journey to building my first telescope by Michael Moller

Telescope Making > ATM Diaries 3

The journey to building my first telescope
By Michael Moller - September 2014

I became interested in ATM (Amateur Telescope Making) sometime after buying my first telescope and joining ASSA in 2012.  In 2013 I started working on photographing the objects in the ASSA-100 deep-sky list, which caused me to put my ATM ambitions on hold for the time being.

At ScopeX 2013 I found the ATM exhibitions particularly interesting and again resolved to take up an ATM project in the future.  At the time I was deep into the ASSA-100 challenge and I did not imagine that I would get to it before around mid-2014 or so.

That winter the weather was nice and clear and to my surprise, by the end of August, I was nearing the end of the ASSA Top-100 list.  By that time I had acquired a rather nice, second-hand, 8-inch Newtonian telescope on an equatorial mount.  It was a marked improvement over the 6-inch I had started with – and part of the reason I managed to get through the ASSA-100 list so quickly.

I was finally ready, and had the time to tackle my first ATM project; but what to build?  First-timers to ATM usually tackle something like a 6-inch Newtonian reflector on a Dobsonian mount, but as I already owned two nice deep-sky instruments, this seemed like a step backwards.  One option was to build a bigger, 10-, or even 12-inch Dobsonian, but I found the scale of such a project daunting.

After some research online I came across a telescope design called a Schiefspiegler. This unique telescope was designed by the German, Anton Kutter, in 1953, and the more I read about it, the more I became convinced that this was the perfect telescope for me to build.  The construction was only slightly more complex than a Newtonian, and the small aperture and long focal-length would complement my short focal-length telescopes nicely.

So it came that on the last day of August 2013 I paid my first visit to the ASSA ATM class at Parktown Boys High in Johannesburg to discuss my project options. There I met Dave Hughes, one of the instructors at the class, whom, himself having built a Schiefspiegler to the exact specifications to the one I had in mind, not too long before, got me going on an unexpectedly quick start. The small aperture meant that some spare glass was quickly found in a cupboard somewhere, and I left class that same afternoon with two freshly cored glass disks, ready to start grinding.

Looking back, everything went surprisingly quick after that. The small aperture and long focal length meant that shaping the mirrors required surprisingly little grinding. Working only Saturday afternoons, I finished the fine grinding by the end of November. At this point the project became more than just a weekend pass-time as I became more eager to finish the scope. I started working evenings and more hours over weekends. Next, I had to polish out the fine pits left by the grinding process using pitch laps which Percy Jacobs had prepared for me at the ATM class.  This had to be done for both the mirror and the tool of the grinding process, as the tool would become the secondary mirror of the Schiefspiegler.

This felt like it took forever. During the grinding process, some progress could be measured every few hours by measuring the sagitta using a plunger micrometer.

Hours of work polishing left a barely observable difference on the surface of the two would-be mirrors. To keep myself motivated I took daily pictures of the mirror surfaces through a microscope, using my cellphone camera.  After at least an hour a day, sometimes much more, for two weeks I finally had the two mirrors polished out.  A Foucault tester which I quickly knocked together showed that the primary mirror had drifted away from a perfectly spherical shape during the polishing out ordeal. After some email advice from Johan Smit I adjusted my stroke and quickly returned the primary to the correct spherical radius of curvature. By this time I think I was getting a 'feel' for the glass, so matching the convex secondary to the primary went very quickly as well. While the only 'logs' I kept were the few pictures I had taken along the way, I don't think figuring the two spherical surfaces took more than a day or two.

Up to this point the mirrors had taken up all my attention and I had not given the construction of the rest of the telescope much thought. Christmas had arrived and I had a week off to do some construction. I had saved an empty coffee can which I had thought would be the ideal housing for the primary mirror, but I still needed a long tube to house the secondary and the focuser. Online searches and even a visit to some local aluminium extruder was disappointing. The only tube diameters available locally were either too small or too large.  I finally happened on a galvanized steel gutter down-pipe at the local hardware superstore which looked like it might do the job.

Now while I'm fairly practically minded, I always consult my wife Robynn when it comes to things aesthetic. After discussing the technical aspects with her, we came up with a sketch of a light, femininely curved, open-cradle assembly which Robynn liked and I thought I could construct. (As opposed to the squat square box shape I would have gone for had I relied solely on my own devices.)

By New Year's the telescope was almost complete. Over the next week I constructed the focuser, and applied some varnish to the wood. The focuser turned out looking very steampunk, which inspired me to continue the theme and add some more copper trim and brass screws just for the look.

The Schiefspiegler turned out with so much personality, that my initial plan to simply use it with one of my exising mounts just wouldn't fly. By February I had decided to build it its own tripod. The easy way would have been to use standard door hinges between the legs and the platform, but I felt this would spoil the steampunk motif, so I designed it with a intricate embedded wooden hinges. It still only took one weekend to complete.

The reaction I get when people see it for the first time is often astonishment at how simple the design is. Even old pros joke that it is too simple, and I hope that its simplicity inspires newcomers to give ATM-ing a try. This telescope virtually built itself. It is like it was going to become what it became regardless of who made it. I was just lucky enough to be there when the time for its becoming arrived.

Michael Moller

 
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