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[ATM] 20incher with segmented and ribbed mirror at 12Kg
Hello all
In a recent discussion on the German ATM newsboard astrotreff.de the dutch
amateur Willem van Nood has introduced his experimental 20 incher with a
segmented and ribbed mirror:
(text in German but also some pictures)
mirror making:
http://www.astrotreff.de/topic.asp?ARCHIVE=true&TOPIC_ID=36400
polishing and first foucaults:
http://www.astrotreff.de/topic.asp?TOPIC_ID=42278
telescope and first light: http://www.astrotreff.de/topic.asp?TOPIC_ID=49760
The telescope features a honeycomb ribbed mirror at 3,6 Kg weight. The first
attempt to make the slumped mirror front in one piece in a homemade kiln was
not successful, so Willem used a smaller kiln with better temperature
control to slump nine front segments individually and glued them together.
Although I would have imagined (from hearsay, not from my own experience)
this could never work out I was surprised to see the pretty spherical
foucault picture (second link) with some printthrough and segmenting.
Willem took it to a paraboloidal shape and sent it off for coating but was
dissappointed to recieve it back with a surface shape tending more to
spherical again. My first thought was this must be due to the glueing, but
you'd probably expect to see a distinctive grid pattern again and Willem
didn't write anything about that.
Also very interesting is the radical mount shown in the third link (weight
without mirror ca 9Kg) which would probably best be described as a Holcomb
type mount as shown on Mel Bartels homepage. It is designed not necessarily
to deliver smooth tracking for planetary observations but a stable and very
light platform for observing deepsky objects at rather small powers.
Though you probably cannot call this experimental scope a complete success
at this stage, as it delivered worse images and contrast than the 10 incher
also present at first light, I feel it might be of interest to this list
nonetheless, especially for the "boundary pushers".
Some numbers:
diameter 508 mm
f-ratio 4.6
thickness of front glass surface 4 mm
thickness of glass for honecomb structure 2 mm
mirror weight 3.6 Kg
telescope weight all inclusive ca. 12 Kg
Any comments and suggestions are highly welcome, I'm sure.
Andreas
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