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Dale Keller built this 10 inch F5.6 newtonian reflector using Coulter optics. The
full-thickness mirror was produced in 1980, when Coulter was known for their high
quality. The tube is sonotube with shallow foam weather-strip baffles. The primary
mirror is mounted in a homemade aluminum 9 point flotation cell. The 1.83 inch
diagonal mirror is mounted in a Kenneth Novak holder with a
homemade brass curved-vane spider.
This size diagonal was selected to give an 18% (by diameter) obstruction of the primary
mirror. This produces a high contrast image at the expense of the 100% illuminated
field of view. The focuser is a 2 inch low profile helical type. The finders are an
8x50 straight-through and a telrad. Three handles are mounted around the tube near
the focuser for convenience in pointing the scope.
The telescope was optimized for visual use using
Newt version 2.5 software. Newt is a Windows
program which ray traces a newtonian telescope and helps you quickly choose the
optimum diagonal size, focuser height and diameter, baffle positions, and many other
things.
The dobson mount was thrown together from scrap plywood 18 years ago with the
intention of making a nicer mount shortly thereafter. That stayed on the to-do list
for many years. (See the new and improved mount below.) The original teflon and
Ebony Star azimuth bearing was replaced with a
lazy susan
bearing with an adjustable friction brake. This works fairly well - the adjustability
is very convenient. The drawback is that it makes too much noise. It's embarrassing
to have your scope squeak loudly at a star party. Oiling it helps, but also makes the
dust stick worse. I would recommend staying with the teflon and Ebony Star bearings.
There is also a friction brake on the altitude bearing. These
brakes are wooden 1 by 2 boards mounted on a pivot with a
knurled knob and spring to adjust them.
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