Re: [ATM] Re:(ATM) F/10 or F/8?

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

Some fellow in the Northern Virginia Astronomy Club
(Greg Wolczansci? if that's the right name, then I
probably murdered the spelling) made a 6 inch f/12
with a tube that broke into 2 sections. He had four
plastic PVC pipes glued into the corners of his
square-plywood tube, then he sawed the whole thing
right in half when it was all dry. Then he put some
dowels, sanded to fit perfectly, into the tubes, so
the whole thing fit together perfectly, and remains
collimated perfectly. Then he used clamps like they
use on steamer trunks to clamp the two halves
together. This way, you have two 3 1/2 foot parts,
instead of one 7 foot tube. I don't recall whether he
parabolized his mirror or not. Images were fairly dim
in comparison with my 6 inch f/8. This is not a
problem on the moon or venus or jupiter.

In any case, Gary's scope worked so well that I stole
his idea to make an airplane- transportable and
breakdownable telescope of my own (6 inch). Mine is
unbelievably ugly, but it works. His was fairly
elegant.
Guy

--- Mike Lockwood <melockwo@uiuc.edu> wrote:

> First, consider the longest length of the tube that
> you're willing to 
> set up and transport.  That will determine the
> highest focal ratio 
> that you can go with.
> 
> Second, if you're working without assistance from
> another experienced 
> mirror maker, a 6" F/10 or F/12 spherical mirror
> will perform well and 
> won't be too hard to make.  (If it's smooth, it will
> provide better 
> images than you think.)  If things go well, you can
> always spend a few 
> minutes parabolizing and get fairly close.  If you
> can get instruction 
> from someone, then F/8 or less will be easier to
> handle, especially 
> interpreting the Foucault shadows and taking zonal
> readings.  You 
> don't have to take readings if you're just testing a
> sphere.


Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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