Dale Keller built this 6 inch F11 planetary newtonian reflector. The mirror was
made by Stellar Optics of California (I don't know if they're still in business).
The mirror is mounted in a homemade aluminum cell. The adjustable diagonal holder
and brass curved-vane spider are also homemade.
The telescope was optimized for visual (planetary) use using
Newt version 2.5
software. The 1 inch diagonal gives a primary obstruction of 17% (by diameter)
for high contrast. Eyepieces are held in a low profile 1.25 inch helical
focuser.
The tube is sonotube covered with fiberglass for a very smooth
finish. The problem with this long thick tube is it's high thermal inertia. It
takes a long time to cool down.
Originally, the tube was fully baffled using cardboard rings mounted in 3 long
wooden trim strips. The baffles did block out unwanted light as intended, but
they introduced another problem. Warm air moving up the tube wall was forced to
move out into the light path as it went past the baffles. This produced terrible
tube currents which never seemed to stop.
I could have modified the baffles by placing cutouts near the tube walls, or
drilled large holes in the tube walls, but I took the simple way out. The
baffles were removed, and the inside of the tube was roughened and painted Ultra
Flat Black (Krylon spray paint). Tube currents were reduced, and image quality
improved.
The mount is made from heavy steel tubing and pipe. The equatorial head uses
pillow block ball bearings to hold the 1.5 inch steel shafts. Simple wooden
brakes with screw clamps are used on the shafts. A clock drive may be added
someday. The mount weighs about 110 pounds, which makes it less than portable,
but very stable.
This telescope performs very well for planetary work. Small details have been
seen on Mars and Jupiter, even through Denver's notoriously unstable air. We may
be above much of the atmosphere, but we're also in the spillover area from the
Continental Divide, so we get constant turbulence.
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