[ATM] What to do next

[Jay Kirkland <jaykirk2@compusmart.ab.ca>]

I think that it's amazing that you're making your own mirror.
That's
something I have yet to do. I've probably done everything else, tho,
and the
first thing I'd suggest is, if you haven't already got it, order
Kriege and
Berry's The Dobsonian Telescope, A Practical Manual... It's a
great guide to
everything you need to know about building the rest of the
scope. It's only
a starting point, however. Miuch of the information is
pretty old, and
searching through the ATM archives for specific topics like
diagonal mirror
size, tube size, and primary mirror cells (see PLOP) will
bring you a couple
of decades of new info. But this book is simply
invaluable.
Mel Bartel's is one of the great treasures of amateur telecope
making
and his site is also totally invaluable. The very best thing I've
read
lately, tho, is the beginning of his article on the "tri-lateral" in
the
current issue of S&T. Decide before anything else what you want your
scope
to do and design it accordingly. My 20" is a Kriege/Berry style Dobs.
It's
got a beautiful mirror from Ed Beck (?) at Enterprise Optics. But
even
building the scope as light as I could, it still needs wheelbarrow
handles,
ramps, and a truck to move it. And thus gets used far, far less
than it
deserves. A couple months ago on Mel Bartel's site I stumbled
across photos
of his trilateral . That a 20" could be light and easy to set
up and move
and use was a revelation.
My re-build is based on all the
basics from Kriege/Berry. Specific
components are all based on what I'm
gleaning from the ATM group. The
current re-build was inspired by the
tri-lateral, but because it's an f 5.7,
I'm sure the truss is too long and
narrow to be stable. So the scope's
become a twin-truss quadrilateral. It
looks not quite like anything I've
seen before, but it's all based first on
Kriege/Berry.
Their book is what you need to not just read but really
absorb next.
Then decide what kind of scope you want. I had some
ill-founded concerns
about vignetting that NEWTWin was warning me about. I
find Sam Brown's in
ancient All About Telescopes the instructions for
laying out your optical
path full size on paper to be tremendously helpful.
Check out a thread a
couple months ago about Vignetting or NEWT on this ATM
group. What you want
to do with your scope will determine which eyepiece(s)
you will use most.
The eyepiece will determine the size of 100%
illumination, which will
detrmine the size of the diagonal, tube ID,
focuser, etc. A scope optimized
for the deep sky and a Nagler 31mm Type 5
is not going to be optimized for
viewing Mars. Once you've decided what
kind of viewing you want to do, the
rest of the scope's design will follow.
Even if you make a scope following
Kriege/Berry to the letter, you will
still end up with a fine instrument
like 1000s of others in use all over
the world, and a copy of the finest Dob
commercially available. But if you
have specific need, you can easily
incorporate them as you go, or go with
something completely original. But
the reason there are 1000s of Obsessions
and 10,000s more clones all over
the world, the design works.
You can check
out some other amazing improvisations of the classic Dob
by following the
link on Mel Bartels' site to Frederick Gea's French
Telescopes.

Jay




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