The Bottom Of The Rocker Box
...is painted with titanium-oxide-based bright white paint. John Dobson
mentioned that this paint should not be used (in his opinion) on telescope
tubes because of its ability to reflect infrared. It seemed like it might
actually help out, though, on the bottom of the rocker (and any other
down-facing surface) so ... I have no idea how much this contributes to
thermal stability (probably very little if any) but it makes for a good joke.
One of the main reasons for the design. I've have (as far as I know) the
largest three-vane Protostar spider ever made, and it has been a great
performer. I didn't want to give it up, and the best solution for using
it turned out to be the "full" top cage you see here. Diffraction spikes
are almost invisible most of the time.
An ion-deposition coated, very smooth 2.1-inch secondary supplied by
Crazy Ed Optical. Though I already had a good secondary, this one actually
showed visible image improvement.
They're 2-1/4" diameter (57mm) .090" (2.28mm) wall aluminum. According to
Kriege's stiffness calculations, that's about three times as stiff as
eight one-inch truss poles, but don't let that fool you: the rigidity
of the truss comes from the tube's arrangement in triangular supports, not
strength of materials.
Two-tube designs rely almost completely on the material itself, and even
with three times the material strength, it's still a weaker design.
Not important, though: it's still more than strong enough (as it turns out).
I used an old Orion 12.5-inch f/4.8 mirror I've had for many years; it's a
decent piece of glass and tested out around 1/4-wave at Chabot, so I've seen
no reason to get anything more spectacular. It's two inches thick.
The cell is a kludge; the mirror support is an old Novak I got from Jim
Brunkella at RTMC, adapted to have pads behind and RTV holding it only from
the sides. The results seem good, but I'm still uncertain about the idea.
The lower portion of the cell (where it joins the rocker box) is 1x2
White Oak struts (very dense and rigid but with the thermal characteristics
of wood) that emulate a tailgate. They are, however, glued in and the mirror
must be removed from the front (not hard at all).
I may yet put on a front baffle, but I like the open ventillation
as it stands.
I'm intrigued by Bryan Greer and Alan Adler's idea about boundary zone
abberations and have a 'back of the mind' plan to try a small fan across
the face. More on this if I get around to it...
I'd estimate around $100 for wood and hardware. I already owned the cell
($10) and spider/secondary mount (~$100). The teflon was part of a $10
purchase I made some years back, and the ebony star was a gift, but would
probably add another $10.
Wastage of various materials probably tacks on another $50 or
so. I screwed up a *lot* of things...
We run my our own server for timocharis.com (and shallowsky.com,
kafkasoft.com and loseloose.com); an 800 MHz Via with Debian Woody
(kernel 2.4.20) and Apache (along with all the other usual utilities).
The picture referenced on my home page is a bit out of date, but still
reasonably accurate and fun. Sooner or later I'll get around to
picturing the latest "secure" improvements.
For all you timocharis watchers, the P200 finally died
an ignominious death, but it was a good server while it lasted,
and some of the components labor on elsewhere. In between, it lived
on an old Mac 7200 and then a Celeron 1GHz..
If anything goes wrong, it's My Fault, not Linus Torvalds'.
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