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9.5 inch F8.4 reflector completed in 1961


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About this observation
Peter Anderson
Time of observation
13/10/2018 - 15:00
9.5" F8.4 reflecting telescope
Observing location
Brisbane Australia
Standard camera
Not relevant

Telescope completed November 1961 - images early in 1962.

After my 6" telescope in 1958, I wanted something bigger. With the recognised standard of a 1:8 thickness to diameter for conventional mounting, that I dare not exceed and only 1" plate porthole glass available in Brisbane, I sourced 1.25" thickness glass in Sydney.  This was in the days of plate glass and my 10" F8 mirror proceeded smoothly until final figuring when it exhibited a turned down edge, common for hand held mirrors.  So it was either back to the grinding process or mask off the last quarter inch which was done with a special mirror cell.  ...and so it became a 9.5" F8.4. The diagonal is quarter inch float plate.  Several strips of the required width were purchased and snapped off in the 1:1.4 proportion and tested on a master flat.  Out of perhaps a dozen pieces one or two might be acceptably flat. The corners were knobbled off underwater with pliers and then ground down to an approximation of the shape required to produce a near circle when viewed at 45 degrees. (My 6" had retained a rectangular diagonal.) This one had three rings supporting the diagonal to eliminate diffraction spikes, but at the cost of a faint fuzz of scattered light around the image. The rotating eyepiece turret is another feature. Mounting is a simple alt-azimuth, but very smooth with a ball bearing race in the azimuth. 

It performs very well optically and mechanically, and I still have it as an 'outside' telescope.

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