41-cm Reflector Telescope
The 41-cm reflector telescope was completed in 2003 but a few aspects of the telescope is not satisfactory:
- Problems with main mirror: Not round, sides not square and the mirror has been scratched during aluminizing by the aluminizer.
- Motor gearboxes good enough for visual viewing but not CCD work.
- Focuser stepper motor not strong enough.
- Telescope is too high for the current store which causes it to loose it's alignment everytime it is stored. Alignment must therefore be redone everytime before it can be used.
Acquisition of the glass
The 25 mm thick glass was bought at PG Glass since no suppliers of telescope glass exists in South Africa and to import it was too expensive. They have been asked for 41 cm round piece of glass which in hindsight was not a good idea. It cost about R800. After receiving the glass I discovered that the glass was not round. In one direction it was 2 to 3 millimeters longer which meant that it was slightly elliptical. A second problem is that the sides is not square which causes problems when the mirror hangs in mirror cell sling. It causes the mirror to move away from it's supports. Thus if one decides to use such glass, buy it square and cut the mirror yourself. At that time however I did not have a machine to cut a round mirror from the glass and decided to live with the problems of the glass for the time being anyway.
Making of the mirror
The mirror was ground and polished by hand. The curve was ground with a tile tool made from dental plaster and tile squares epoxied to it. Eventually the first set of tiles ground away and a second set was glued on which saw the grinding to completion. A pitch lap was made from dental plaster and bitumen. Cerium oxide was used to polish the mirror. Eventually the mirror was complete according to the Foucalt and Ronchi tests. The mirror was taken to the aluminizer to be aluminized. When I picked up the mirror at the aluminizer the mirror looked beautifull but when I examined it up close at home was horrified that it was full of scratches which was certainly not there beforehand. I suspect that the aluminizer used a contaminated rag to clean the mirror since the scratched is curved like one would expect from cleaning the mirror. But the damage was done and I decided to live with it for the time being. In spite of the problems the mirror still gives good images. One can see far more with it than smaller telescopes.
Photos
Below is pictures of the telescope. Click on the thumbnails for a larger picture.
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| The 41-cm main mirror | Stepper motor with gearbox | Stepper motor with gearbox | Old storage of telescope | Old storage and track | Mirror box with bearings |