This
is a 16" Dobsonian reflector telescope. I built in in 1987 and it's still
in excellent condition throughout. The polished diameter is actually
16.25"; the focal length is 79.8", resulting in an f/4.9 focal ratio.
A fast focal ratio, f/5 or below, really brings out the wispy details of nebulae
and galaxies relative to the stars.
Interestingly,
the larger mirror increases the brightness of extended objects more than point
sources - such as stars.
In
the foreground is an Astrophysics 6" f/8 refractor. It is on an
"equatorial mounting", which follows celestial objects by rotating the
telescope about the polar axis. You can see the polar axis pointed up at about a
40 degree angle due to the latitude where I typically observe.
On
top of the telescope is a piggyback platform that holds a TeleVue Pronto, and a wide variety of
camera / lens setups.
Here's
a closer look at the Byers 812 mount and the Schaefer declination assembly. You
can see the 40 degree inclination of the polar axis even though it's inside the
black cone. A trusty C-clamp holds my declination drive motor in place after I
accidentally stripped some threads. The large steel weight near the lower
end of the declination axis balances the telescope about the polar axis. Moving
the telescope end-to-end in the split-ring clamps adjust balance about the
declination axis.
The circular part of the base can be tilted to match the location's latitude. A worm gear inside the
base drives a 30 degree segment of a 12" diameter tooth gear to achieve
smooth, reliable tracking.
The
primary mirror of the reflecting telescope is almost 16.5" in diameter, of
which 16.25" are coated with aluminum that is 92% reflective. The flash
photograph makes it look like there is a lot of dust on the mirror. However, it
covers only a small percentage of the surface area and reduced the contrast of
the image only slightly. You can't see "specks of dust" looking
through the telescope.
It's much better to
clean a mirror very occasionally, rather than risking a scratch in its
micro-thin reflective coating. About every 10 years, the aluminum needs to be
stripped and recoated. Even the mirrors of world-class observatories receive a
new coating every 5 to 10 years.
