Re: [ATM] what to do next Part 2

["Bob May" <bobmay@nethere.com>]

A Couder Mask (or the Ritchey version where each mask has one pair of holes)
is easy to make.  Just grab TEX for one and that program puts out a
PostScript file for sending to a PostScript printer that will provide all
the locations of the holes for the mask.
In addition, the simple use of a set of dividers or compass (divider with a
pencil on one end) drawing arcs on the mask material (the thin
cardboard/posterboard of the art world is fine) and then cutting out
alternate arcs is all that the mask is.  The radii of the edges of the arcs
does want to be known within a 1/8" or so.
Now that you know how long your focal length is, you can figure out where
the primary is going to approximately be compared to where the secondary
parts are going to be.  Set the primary so that it is going to be about 2"
into the end of the tube and drill for all of the secondary parts and place
them.  ONCE you have the mirror FINISHED, you can then do the drilling for
the primary stuff and then trim the end of the tube to where you want it to
be.
Vignetting is where the edge of the light path is obstructed (vignetted) by
something and the program will say which part is doing the obstruction.
Minor amounts of obstruction don't affect the performance of the telescope
but larger amounts will.  Remember that 40% obstruction is about 1 magnitude
of light loss.   In addition, the light loss is at the edge of the aperture
where the light is often mostly lost at the edges in the coma tail of the
image.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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