In this part of the tutorial we make and install the secondary mirror assembly. This is the little mirror that directs the light out of the tube and into the eyepiece.

part 1 of this tutorial (the beginning) is here

• Parts list For the diagonal mirror assembly :
• 18 inches of threaded rod - 8-32
• nine 8-32 nuts for the threaded rod
• 1 piece of one inch diameter dowel that is 2 inches long
• 1 diagonal mirror

We want that diagonal mirror to be centered in the tube. And we also want it to be placed so it is in line with the focuser like you see in this picture.

Cut your wooden dowel to a length of two inches. Then cut one end of it at a forty-five degree angle.

Drill three holes in that wooden dowel piece. They are around the circumference and evenly spaced.

They are like this. And you will be placing a threaded rod into each of them. But not yet!

Apply an epoxy to the parts and attach them together.

Center that wooden dowel on the mirror. It is centered both top to bottom and left to right.

Cut three pieces of your threaded rod so that they are longer than half the tube diameter. In my case I cut them each to six inches long. Now place them like this with the mirror mount.

Place that assembly on your tube like this. Align it so the 45 degree angle will direct the light directly to your eyepiece.

This picture doesn't show the secondary mirror yet mounted on the wooden dowel. But it should be on yours.

Now we need to figure out how far down to drill the holes so the mirror will be centered on the eyepiece focuser.

Measure the distance from the drilled holes to the center of the secondary mirror. Then subtract that from four inches.

That number is how far down you drill for the threaded rods. This measurement will place the center of the secondary mirror at the center of the eyepiece focuser.

So it will look like this.

Go ahead and drill those holes then install the rods and install the secondary mirror assembly.

Do not glue anything. Each threaded rod gets three nuts and with these nuts you can adjust the position of the secondary mirror so it is exactly in the center of the tube and lined up perfectly with the eyepiece focuser.

There you go. It looks good.

Let's continue and finish the telescope tube assembly

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