[ATM] Dob vs Eq mount

[scott.e at quicksurfer.com (Scott Ewart)]

    The split ring I'm building (12.5") is mostly stainless steel.  I tried
to keep the weight down, but it's turning out to be pretty heavy.  The key
to keeping it light (as with just about any truss scope) is keeping the UTA
light.  The lighter the top, the lower the dec axis.  The lower the dec
axis, the smaller the split ring can be.  Do you want a rotating tube or
upper cage?  That's more weight.
    Of course, you can add lots of counterweight, like JMI, but that's
cheating (not ideal).  You can help by making a fast scope, too.  But with a
12.5" f/5.5, rotating tube, I've managed to keep the split ring to 32.5"
O.D.  Not tiny, but smaller than most 8- or 10" rings I've seen.  It's
pretty heavy, but I'll need almost no counterweight.
    And if you're looking for simplicity, look elsewhere.  There are lots of
books out there on how to build a Dob, and a Poncet platform isn't too
complicated.  But this is taking a while.  Lots of engineering, lots of
thought, lots of time.  My OTA is done, the mirror's done, but I'm still
working on the mount.
    Ask just about anyone who's built one of these "If you had it to do over
again, what would you do differently?", he'll say "Build a Dob".  I hope I
never get to that point.  I'm still having fun.  And when it's done, it'll
be a work of art.  I just hope it works.

Scott Ewart


----- Original Message ----- 
From: "Richard Brodie" <richardbrodie@optusnet.com.au>
To: <ATM@atmlist.net>
Sent: Monday, March 01, 2004 9:36 PM
Subject: FW: [ATM] Dob vs Eq mount


|
| >
| > Richard ; would a split ring mount , meet your ultra light
| > requirements???.
|
| I think so.  Most (all?) of the split rings I have seen on the web are
| fairly large wooden things.  The design I have in mind would be alu, and
| more compact than what I have seen.  It would still have a larger foot
| print than a dob, but not overly so, and it may be lighter.  Trouble is,
| at this point in time it is still conceptual and as I haven't seen
| others do it yet the performance is unknown.  It may suffer from flexing
| or more likely vibration, but I should be able to engineer these out
| over time.
|
| At this point in time I will probably proceed with designing an eq mount
| as it will be an interesting project.
|
| Richard
|
| >
| > >
| > > Is there a particular reason(s) for this?  I would have thought that
| an
| > > equatorial (eg split ring) would be just as easy to construct, just
| as
| > > compact but easier for tracking and better for photography.
| > >
|
|


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