8" f/8 Long John

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Primary Mirror (self made): 
Material: Duran 50
Diameter:            8" (208mm)
Thickness at the edge: 1,4" (36mm)
Focal length: 65,3" (1659mm= f/7,97

Secondary mirror:

1,6" minor axis, 94% reflection

OTA: 38lb
Telescope total: 58, lb without eyepiece, with finder scope

8*2” (50mm) 2nd hand



This telescope is my first self made one. When starting to built I already had a 6” Newtonian on a German mount (TAL 2with Vixen GP-E). The first self grinded mirror should become bigger (8”); to get not too much trouble while figuring I decided to make it f/8.

When making the mirror I did not had a digital camera, therefore there are no pictures of the making available. 

The mirror was bought from the VdS (the association of the German sky observers), Thomas Heising. At the telephone Thomas already told me, that the blank have some failures, but I was really horrent when seen the big chips. I was that shocked that I asked my neighbor to make some pictures for reclamation. At the end I took the blank and it become a really amazing mirror!    


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While making the mirror I wrote a log, that can be seen here (unfortunately in German)


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The mirror cell is a simple one with 3 supports. As the diameter/thickness ratio is 6 to 1 this is sufficient. The basis is a board of baltic birch plywood, 0,5” thick. Collimation will be made with 3 butterfly nuts against springs. For faster cool-down I made some holes in the board.

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For transportation purposes I decided to find a way for splitting the tube. The side boards made of Ό” plywood are glued and screwed on wooden square trusses (0,8”). On one piece the trusses stick out approx. 4”, the trusses can be stuck in the other piece and fixed with 4 butterfly bolts. The result is a really stable connection, stable enough to keep collimation.
hoehenrad01.jpg (80753 Byte) The diameter of the altitude bearings is 10“, this is not very much, but this eases transportation, it is not necessary to unscrew them.  Ebony Star floats on Telfon. On the picture you can see the butterfly bolts easily.
rocker01.jpg (107542 Byte) Due to the strong construction the balance point is relatively high, this needs a high rocker box. Long hours of sawing, rasping and filing were spent to built this “peace of art”. Unfortunately it became instable. To make it more stable I affixed some stilts – like at a gothic cathedral.
boden01.jpg (107217 Byte) The diameter of the ground board is approx. 16”, not much for a rocker of this high. It is based on a massive triangle made of 1” beech plywood. This is really stable but also very heavy. My saw came in trouble with this kind of wood.
deckel01.jpg (76352 Byte) The focusser I bought – as the finder – second hand. On this way I got the JMI NGF-DX1 for half of the normal price. I built from plastics and black cloth a light protector that is mounted directly at the focuser. Looking over the eyepiece you’re seeing only absolutely black, this help you for another 0,2 magnitude when searching for faint fuzzies!

I integrated a sun filter in the dust cover. While using it, the cover shields the finder, no risk to burn your head by accident.

staubschutz01.jpg (73629 Byte) For transportation purposes I built an other cover. This cover the lower half of the telescope. Ulrike mentioned it looks like the cover of a toilet – I found no reply at that moment. Nevertheless it is practically and fits perfect. 

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