My ATM- Story
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At the ITV2001 – this is the largest telescope meeting in Germany, held at the “Vogelsberg”, approx. 60km away from Frankfurt – I had contact to the ATM scene first time. This was 4 months after I bought my first telescope, a nice 6-inch Newtonian (TAL 2). I was really fascinated and unbelieving that it should be possible to built a telescope mirror with simple equipment by an amateur. To built a Newtonian telescope with a Dobson mount … o.k. this appeared ambitious to me, but even a mirror? I was aware of the extremely small tolerances (I did not forget all that I’ve learned at university) and therefore amazed to find this at the ITV. The ultimate telescope was Stathis Kafalis Kyklopas, a 24” lightweight Dobson – without any doubt.
While looking about information to my TAL2 via Internet I
found the TAL-forum of Armin Quante, there I felt in good hands. I met Armin
personally at Erlangen two times, business trips have some advantages
(especially if I have not to travel myself). His tips were a big help for me as
a novice; especially how to handle with a German mount and how to find faint
fuzzles at the sky. I met Armin again at the ITV.
When Armin mentioned, that he had started to grind an
astronomical mirror I thought: really
amazing, if I could do the same! The germinal for something own was created.
Armin himself was engaged with reconstructing of his house, his project made no
progress for some months. More and more my desire grows to try it myself.
Despite of disbelieve to myself I ventured it in December 2001.
I ordered an 8“ mirror kit at the VDS (the association
of the German sky observers), this won’t happen if Armin did not cajoled to
me. (there fore the guilty person is found).
With support of the German ATM Mailing list – especially from Martin Trittelvitz and Stathis Kafalis – and some ambition together with carefulness it became a success. 8 weeks after starting with grinding the mirror was figured. Building the telescope took approx. another 8 weeks. My first own telescope, an 8” f/8 named LongJohn was ready. As a newcomer I was not confident on my own judging of the mirror, at the ITV 2002 Stathis did me a favour and made a start test. “Only 5 of 100 mirrors are as good as yours” he said; I was really happy and proud on myself.
Now I would like to build a lager telescope. But how to explain to Silvia, the best wife of the world? I already had had my TAL2, a 110mm (4,3”) Kutter, the 8” and a 4”Maksutov (bought for photography and travelling – this was the intention but it didn’t happen). The Kutter (an off-axis mirror telescope) was a really fine telescope, but compared with the long 8” Dobson it succumbed. The image was a bit more aesthetic for purists, but with much less light-power. I finally sold it to be able to finance my
a 14“ Newtonian. After spending some time with searching
for a good source I bought a blank by Sven Szelasek. Original Pyrex from
Corning, a blank like form a picture gallery. Coming from 8” f/8 going to
14” f/5,3 is a big step, but Stathis encourages myself to try it, without this
I would have tried a f/6 – a size that need a ladder for observation.
While I had no problems with the first mirror, I was faced
with problems with the second: scraps while polishing and a fortnight-dance with
figuring. Fortnight? This sounds like a short period. In fact I made 3 to 4
tries to find the right figure every day. Stolidly – like I can be with the
intention to figure with the 14” fullsize tool. After 3 days I reached the
Raleigh-criteria, but it won’t to become better. Finally I was successful, to
be honest with some luck. Testing with a 6-zone Coulder mask I measured Lamda/11
wavefront as average. I stored the mirror on a shelf that was fixed with dowels
at the wall. ´
Now I started to build the telescope. At the ITV I realised some very clever designs; the friendly telescope builder Roland Krebs explained me all the details of his telescope. I decided to use his concept for the mirror box, other details are from Stathis telescope and own findings.
Floating 18-point cell, mirror box and secondary spider were already ready, when it clanked in my house some Sunday morning. I went from room to room to find the reason. When reaching the basement I found it: the weight pulled off the dowels out of the wall, the shelf fell on the tiles and all the stuff on it: the tile-tool, the pitch-tool, some glasses with Carbo, the half-builden Finder Newton … all was now broken lying like chaos on the floor. It took a while until I realised: the 14” mirror was on the shelf, too! (see picture) My head felt empty, I was totally without emotions.
I got lots of friendly solace at the ATM mailing-list and astronomical forms that it was clear to me to try it again after a short while. As the 14” Dobson was already started I decided to grind a 14” again. A blank in this size was not available soon, but a 315mm (12,5”) made of Rasotherm. I decided to buy this AND a 14” made of Pyrex. First of all I finalised a 108mm (4,3”) finder Newtonian that I started to grind at the ITV, than I took the 315mm to eliminate my frustration. After 5 weeks I placed this mirror at the side and started to make the 14”, this time as f/5,1. 5 ½ weeks later I was ready for figuring. Again I tried it with fullsize tool, after 50 tries with ups and downs (unfortunately more downs) I built an 8” tool.
Experiences I made with other mirrors don’t want to help, all the time the results were different to my expectations. I was frustrated and lamented for my broken mirror. Finally the key for success was only minor changed conditions (2 Celsius higher temperature in the polishing room, the subsize-tool and good fitting pitch). At December 24th at 10.30h I was ready – my Christmas gift. Figures? Better than from the broken mirror. This time the parabola was not (partly) an accident, it was created step by step.
I made only slow progress with the Dobson, I’d problems to get all the small things that I needed for building. In Krieg&Berry’s book you often can read the sentence ”buy it in your local hardware store”, I couldn’t read it anymore. Nowadays it is really difficult (at least in Germany) to get things that are not fully standard. So I had to improvise a lot. In the meantime I finished the 315mm mirror. 2 weeks after starting polishing again (I’ troubles with scratches) the f/4,7 mirror was ready – all the experiences helped a lot.
In April 2003 the 2nd “first light” stopped my concerns, the mirror is fine, uff!!
All my mirrors are taking 7 to 8 weeks, I thought. I should try to make a 20” to see if this is a general rule for me. Just ready with a project I’m getting nervous, the “glassworm” is starting to twinge. But blanks in this size are really expensive in Germany, much more expensive than in US. I remembered that there is a polish guy who is making blanks (today not very professional) that are much more cheaper. The doom for the next project was starting.
Today I know that it can take more than 8 weeks for me to make an astronomical mirror, especially when you are faced with major problems. This cost effort and motivation. For the 20” I had to spent 14 weeks, approximately half the time for “coming out of the holes I dropped in”. But – I think – I’ve learned a lot.
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