Re: ATM "more normal" scope pix

[Kent Cheatham <cheatham@ionet.net>]

I have a 13" coulter (5 yr old). I just bought it for $600 and cannot even
get the slide tube to stay straight enough for a decent star test. I will
have to make many modifications to correct it (Krajci spring, focuser,
secondary spider (it's 1/4" pig iron!) and vent either the pri cell or rear
of the tube). On the average, were Coulter mirrors good enough to consider
scrapping everything but the mirrors and build a truss frame work in place
of this 150# monster? Or would I be better off using this for what it's
worth now and get a better mirror in a year, to make a lighter truss tube
with?

Kent Cheatham
cheatham@ionet.net
------


Bob Prabowo wrote:

> Hi guys,
>
> I think a truss tube telescope might considered as "abnormal" because it
> doesn't look like a telescope. The first thing that people would think
> of when they hear a word telescope would be a refractor or a Newtonian,
> people think  that a telescope must have a tube.
>
> Last weekend, in the scientific camping program for Junior high school
> students, I brought my 13" and displayed it. It was part of a plan B in
> case the sky was cloudy (plan A was to have a kind of public observing
> session under a bright 3-day old moon sky, and plan B was to conduct a
> telescope making and mirror making class if the weather didn't permit,
> we're lucky the sky was clear.. and brrriiighhtt.)
> Anyway, during the briefing session (where I explained the star party
> rules) I briefly told them that they can build their own telescope. The
> 13" scope was placed next to a Meade SCT, Meade refractor and Tasco
> refractors (do you guys call it Trashco?). Every kid in that room knew
> that the SCT and the refractors were telescopes. But they didn't know
> that the wooden box with aluminum truss was also a telescope (to my
> surprise, some friends from my club also didn't know that it's a
> telescope). The kids asked where the tube was (there were 8 aluminium
> tubes, but apparently these weren't the tube they had in mind).
>
> A truss style Dobsonian might look difficult to build. But it's not.
> I've made two telescopes so far (telescopes only, without the mirrors).
> The 13" is my second telescope. The first one is an ugly 5.6" version of
> Alice :-) It was my first telescope and my first woodworking project.
> I made both of the scopes with hand tools. It wasn't until the
> construction of my 13" was 75% finished that i could afford a jig saw,
> and then an electric drill. But I built it mostly with hand tools.
> When the construction of my 13" was finally finished, I took a looooong
> look at it and said to myself "So, this is how a truss tube telescope
> looks like." That was my first close encounter with a truss tube
> telescope (second actually, the first one was with my ugly version of
> Alice)
>
> Don't let the appearance intimidates you. A truss style scope is not
> more difficult to build than a solid tube one. When you build a solid
> tube scope, you have to build the rocker box and the ground box, right?
> Why not take one more step further and build the mirror box and the
> upper cage or ring? By the time you finished the ground and the rocker
> box you will have all the skills needed to make the mirror box and the
> upper ring.
>
> For a smaller telescope it may be better to stick with solid tube
> design. But IMHO, when it comes to portability and compactness, nothing
> beats truss tube Dobsonian (my 13" when it's disassembled is only half
> the size of my 8" SCT case).  But as to which style one should build,
> it's really a matter of a personal taste.
>
> Bob P. Sumitro
> Jakarta, Indonesia
>
> visit my still-under-construction astronomy and telescope making page:
> http://www.geocities.com/CapeCanaveral/Hall/2670/