[ATM] UPS Modified Scope

[Jay Kirkland <jaykirk2@compusmart.ab.ca>]

	That is a total horror story. 
	If insurance pays for it, I'd go with a spider from Gary Wolanski. I've
found the quality of his products to be first rate. ProtoStar makes
beautiful spiders but despite what their web page would have you believe,
they are not easy to install at all. Your installation (the holes you drill
in the tube) must be pretty much exact from the first moment as there is
virtually no latitude for adjustment. And their install instructions don't
take into account varying thickness between one  secondary and another. Do
note that Mr. Wolanski's 4 vane spiders have offset vanes and that you
cannot use holes placed at 90 degree intervals around the tube. So you'll
have to drill 4 new holes in your tube. 
	If you need stainless, any good model shop sells stainless steel in
varying thicknesses and widths. I wouldn't cut it into a taper or cut along
its length at all, as that will always roughen the edge and create a
thicker vane than you'd want.
	It is however extremely easy to make spiders using guitar string stainless
wire. I used one on my 12 1/2 f6 for years, switched back to my Novack
spider to see what that would be like, was horrified at the diffraction
spikes that I wasn't used to seeing, and quickly switched back to wire. I
used .25mm/.010in on the 12" and .51mm/.020in on my 20". The 12" spider may
be a little fragile (especially as temps here vary  over the year between
-30 F and +90F, the best seeing aways being the former) , and the spider on
the 20" is actually overkill. Mel Bartel's design for a wire spider seems
really complicated to me. I followed the style in Paul's Telescopes for
Stargazing, pg 118. You do need a couple extra inches of tube at the
eyepiece end for that design, tho. Made of a couple small wooden circles,
some 1/4" dowel, and some screw eyes, is all. Doesn't look like anything
remotely professional but once you get used to observing w/o diffraction
spikes or diffraction spread all over everything (see curved spiders),
you'll never go back. Good luck. 

Jay


_______________________________________________
ATM mailing list http://www.atmlist.net/