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<DIV><FONT face=Arial size=2>Hi Fred,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Thank's for the answer.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Eureka! Just located the right size mirror cell at
Astro Parts. to fit the Protostar tube. Damn things are hard to find. Looks like
the fully setup OTA will weigh in at just over 23 lbs so the mount shouldn't be
a problem.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I thought about different tubes. Sonotube -
degrades fairly quickly, is vulnerable to moisture and is relatively heavy,
PVC - very heavy, dries out and becomes brittle, will sag and warp under its own
weight within weeks Aluminum - cheap but heavier, painting the exterior changes
emmisivity characteristics - it would look like a big tin (aluminum) can - needs
alot of work finishing ie. painting flocking etc. The protostar, acording to the
manufacturer, is very rigid, has a 99+% light absorbing to 700nm flocking,
extremely low emmisivity, is easy to cut , drill etc. and a 48 " tube is
only 7 lbs! </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I plan on using caps of the same material on both
ends ( removeable ) One cut out for the Baader Turbo film. It will be
interesting to see if there is any light absorption by the film, they say not.
Worst that can happen is I wind up with a see-through dust cap.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I've done enough gemsone polishing over the years
to know that it is more of an art - the science is in the testing. I made a
1/4 wave many years ago, but a 1/20 wave here in the land of wind and dust ... I
don't think so. Besides the kit costs more that a finished primary and secondary
put together! The mirrors are from Hubble Optics f/4.72 I've seen the test
report and found all good reviews on several ATM forums. Hopefully I won't get
burned.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I mentioned a design program NEWT 2.5. Very easy to
use It was written in the early 90s for Windows 3.1 . Plug in the appropriate
numbers and it calculated all the proper stats and measurements by ray
tracing. Found another newer program last night and came up with the same
results, happy days! Anyway, it will give me a starting point for cutting the
focuser holes and spider. Then I can move the mirror in to optomize for ccd
camera operation with out running out of back travel. I can always add
extensions for eyepiece use. It also showed that I can reduce the secondary from
2.5 MA to 2" with full illumination giving me only a 19% light
obstruction.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>That's the theory anyway. Anyone see any holes feel
free to poke.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Regards,</FONT></DIV>
<DIV><FONT face=Arial size=2>Gary </FONT></DIV></BODY></HTML>