Quote:
Originally Posted by White Rabbit
Thanks Gary,
As I said above I'm just spit balling here so thank you for the detailed response.
Sandy
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No problem! Nothing wrong with spit balling and that's why we are all here.
However, unless you want something that resembles the bridge that
collapsed in Minneapolis earlier this month, don't go hoisting that LB 12
onto an eq mount using rings of any sort.
When you first get a truss pole Dob disassembled, a couple of things
strike you when you pick up the parts.
When you pick up the top end cage, you tend to think, "Boy, this is light!".
When you pick up the mirror and rocker box, you tend to think, "Geeze! This is
heavy!"
That very heavy bottom end you just can't go whirling around in the air. Apart from the
weight, the mirrors are designed to sit in there assuming the scope is on reasonably
level ground. On some Dobs, tip them over far enough and the mirror will
just fall out of the box. It's own weight is what is designed to keep it in there
on the assumption the scope is sitting on the ground.
Some personal views on scope selection having looked through a lot
of them -
Nothing beats aperture. However, some of the key differences between the
low cost Dobsonians and the premium Dobsonians, like an Obsession or
a locally made SDM, is that the premium scopes use very thin mirrors that
are designed to cool down quickly. The thermal mass of a larger, thick
mirror is such that you can spend much of the night waiting for the mirror
to cool and if it is not cool, the optical peformance will suffer. However,
Dobs get away using thinner mirrors than some other designs
by having (hopefully) carefully designed mirror cells (mechanical supports)
that are designed to keep the mirror figured (i.e. stop it from warping under
its own weight).
Strictly speaking, according to their designers, many Dobs aren't
even designed to sit on top of an equatorial table let alone an equatorial mount,
as the cell design is then pushed beyond what it was designed to do.
One other feature that differentiates the premium Dobs from the low-cost
generics is the smoothness of their motion. The best ones have just the
right amount of stiction - what Dave Kriege describes as "buttery smooth".
You push it and it moves without hesitation and you stop pushing and it stops.
So in that regard, premium Dobs have migtrated from simply being an
implementation of a simple and low cost style of mount to what might
be described as a "driving experience". They feel good when you move them
and it gives you the type of control and smoothness of a high performance
car. In my opinion, this 'feel' is as much a part of the expereince as the
view through the eyepiece, because if one is frustrated with the movement, then
it distracts from the viewing.
If you haven't done so already, if you spot a premium truss pole Dob
at a star party, ask the owner if they mind if you could have a look through
it and be allowed to give it a push. Even if you aren't about to run out and
buy one, like the opportunity of driving a really high performance car,
its fun and you appreciate how good things can get.
Were you interested in astrophotography as well, hence the question with
regard the EQ6?
Best Regards
Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au