How to make a Newtonian Telescope part 4: The focuser
In this part we install the focuser assembly for the eyepiece
I do have a video showing this whole process. You can watch that at the bottom of this page. Here is a picture of the completed assembly. This is what we are making in this part. This picture shows the focuser.
This part is pretty easy. It is just a matter of measuring the location of the focuser, cutting the hole and mounting it down. But we have to be reasonably accurate with the distance. Our focuser gives us quite a bit of leeway with this but lets get it within an inch so we are good to go.
When I ran the test setup I found the distance from the mirror to the diagonal was 35 inches. So, the surface of the mirror to the diagonal is 35 inches!
We do have that mirror assembly inside that tube and that brings the mirror three inches from the end of the tube. so we have to compensate for that by adding those three inches.
So now the eyepiece, being exactly where the diagonal mirror is. Needs to be 38 inches from that back end. that puts it exactly 35 inches from the mirror.
Measure that distance off and drill a hole for the focuser assembly. My hole is 2″ in diameter. Test it and be sure the focuser slides all the way in and out easily without getting caught on anything. If you are unsure of this you can drill a practice hole on a scrap of wood or scrap of tube and test it.
Mount the focuser to the tube. Typically you need for bolts. I used 6-32 bolts that are 1 inch long. Washers and nuts go on the inside to hold the bolts.