Re: ATM Collimation tool

[Adam Perkins <scopeguru@yahoo.com>]

Hi,

This has probably been discussed in the archives, but...

My collimation aid is made from a piece of 1.25" sink drain extension. 
In the US, these come in a standard 1.25" O.D. x 6"? Chromed brass type
for a dollar or two.

The neat thing about these tubes is that the outside diameter of one
end is 1-1/4" (to fit in your focuser).  The opposite end of the tube
is flared out to have a 1-1/4" INSIDE dia.  This wider end keeps the
tube from falling through the focuser, and a 35mm film canister lid
fits over it snugly.  

I made my tube by wrapping a strip of paper around the narrow end of
the tube and marking where the strip overlapped itself.  This gave me
the exact circumference.  Folding this strip into four and marking the
creases gives you the location of the thread ends if you wrap it back
around the tube.

The tube should be notched to allow the cross-hairs to be glued into
place, I used a DREMEL tool, but a small file might work.   Just make
the notches about as deep and wide as the thread, or as small as you
can manage.

Pull a piece of (black) thread, across two opposite notches, and apply
a drop of cyanoacrylate glue (superglue) to each end.  It should dry in
a few moments, while you hold the thread tight.  Do this for the other
cross hair and then cut the extra length off and lightly sand off any
glue that seeped out of the notch to the outside of the tube.

The result is a perfectly centered cross hair.

The wider end of the tube has the film lid glued to it.  The center of
the lid (Kodak lids have a little molding mark dead center)  has a
small hole made by heating a thumbtack with a match and melting the
plastic.  Enlarge the hole just enough to be comfortable to look
through.

The combination of the long tube (about 6-7") and small hole make this
tube accurate and provide a fairly sharp view of the cross hairs.

Hope this helps Someone,

Adam Perkins
Covington, Louisiana


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