Making a Sight Tube for Collimation

By Adam Perkins

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.

I added a band of tape on the tube to limit its protrusion into the OTA, This was not absolutely necessary for me but the tube might be long enough to actually touch the secondary in a really small scope.

Hope this helps Someone,

Adam Perkins,
Covington, Louisiana