Hey mate,
Yep, the Hubble optics sets do seem to represent excellent value for money.
I have heard mixed reports about them though. A few have been tested
by Wolfgang Rohr and show varying degrees of Surface roughness
astigmatism and under-correction. The testing done by Richard Berry on
the optic donated to the Cal Poly 18 project is somewhat inconclusive. The last
update I am aware of is that the secondary mirror (not supplied by HO)
was astigmatic and the overall system was highly sensitive to temperature
change so no definitive assessment of the primary could be made at this stage.
The positive is that the problem mirrors were made some time ago so perhaps
the current crop are an improvement.
More on the Cal Poly 18:
http://www.wvi.com/~rberry/calpoly18/calpoly18.htm
If you explore that link you will see that the project shows a great deal of promise.
If you can find it within yourself to look past the image defects resulting from
the secondary (and the fact that the scope itself is one seriously ugly *******)
the core of it is a sub-1m, professional observatory class research instrument.
The results obtained with the prototype so far show that the system can
track to an accuracy of 0.5 arc seconds for unguided exposures of 15 minutes
or longer, but unlike normal drive systems direct drives compensate for
loading due to wind, cables, imbalance etc. It helps that the mechanical
structure of the telescope has a resonant frequency above 10Hz.
RMS pointing accuracy at this stage is less than 10 arc seconds across the
sky just using a basic 30 star model, so this could no doubt be improved.
Dave Rowe designed the direct drives for this telescope so that they could be
replicated by amateurs albeit with access to a decent machine shop. Dan Grey
has developed a version of the Sci-Tech controller specifically for the
purpose though it hasn't been released to the public yet. I suggested to him
a little while back that the motors from Fisher & Paykel washing machines
might be a cheap option for kerb scroungers. Curiously, he was not aware
of them. F&P don't have much of a retail presence in the US but I believe
that Maytag has just acquired the motor technology so this will change.
Anyway, the upshot is that Dan has since had a Fisher & Paykel motor on
the test bench and says that it is indeed suitable for a small telescope. There
is a bit of variation between models in the gauge of wire in the windings in
these motors, some of which which require higher voltage. The last time I
talked with him he was working on a more robust output stage for the driver,
but in essence it's all pretty much just around the corner.
regards
~c