8 Inch Newtonian Telescope on an Equatorial Mount

In preparation for a visit to Mexican Hat, UT for the Annular Solar Eclipse on 14 October 2023, I decided to make a third version of my 8 inch telescope.

This Instructable documents the building of three primary telescope parts: The optical tube, the optical tube ring holders for the EQ mount, and the mirror cell. This was constructed in September of 2023.

1. Aluminum U-channel
2. Aluminum flat stock
3. Hex screws
4. Screws and bolts
5. 3 Small bearings (recovered from old hard drives- see solar projects)
6. 24x36" sheet of thin aluminum
7. Flocking material (black felt with self-adhesive back)
8. Small furniture sliders
9. Two quick latches
10. Existing telescope assemblies

Tools:

1. Roller/Brake/Shear combination sheet metal machine (https://www.harborfreight.com/30-inch-shear-press-brake-and-slip-roll-5907.html)
2. Hacksaw
3. Scroll Saw
4. Drill Bits
5. Taps for threads
6. Combination Wrenches
7. Drill Press
8. Portable Drill
9. Bench Vise

Standard safety for working with metal, gloves, eye and ear protection.

BLUF: Speed build existing optics into a more portable system; timeline less than a month.

I have a 10" Classic Meade LX200 I purchased in 2000. Often it just a little too big to setup, and definitely not easy to travel with. I was working out of the country in 2005 and missed my scope, so I bought an 8" primary and secondary set, and built a working Newtonian from some large PVC drain pipe. Matched with a photo tripod, this was not easy to aim/point.

After the outing in the photo, I came up with a Psuedo-Nasmyth design and CNC routed a much more stable and useable mount for the existing optics. While this was a great demonstration, discussion, and instructional scope, it was still time consuming to setup.

I was going out west to see the Annular Solar Eclipse on Oct 14, 2023, and I decided I wanted to take the 8" optics with me, but without the cumbersome setup. So, this is the 3rd generation scope built, that the same optics will occupy.

A member of the local astronomy organization left a message in a forum about a free Equatorial Mount and tripod. I was the first to respond and promptly picked up the items. The mount was a little oxidized and needed some love and care. It was easily cleaned up and I confirmed that it was fully functional.

This is just the tube. It will become the Optical Tube Assembly (OTA) once we install the mirror and add the secondary and focuser. The tube target is around 10 inches in diameter and slightly longer than 24 inches. Since our spider and focuser are already completed (borrowed from the CNC scope), the 24 inch tube length should suffice. Take the 24x36 sheet of thin aluminum and send it through the rolling machine. This is a manual roller, so you may have to go back a forth to continue to decrease the rolling diameter. I then pop riveted the overlap together, hoping that the overlap would provide additional rigidity.

I designed some inner ribs to support the tube internally. I used my CNC router to cut both plywood and some scrap ABS of various thicknesses. These ribs could also be considered optical baffles, but technically not a mathematically proficient design. The CNC design gave me one solid ring and 10 quadrant arcs. So each layer I cut gave me essentially 3.5 ring layers. I fastened two rings (8 arcs) together with screws.

A shiny aluminum tube is not the best optical choice for a telescope interior. There are a few methods to keep stray light out of the optical path to increase contrast. The most common is flocking (non-reflective coating that absorbs stray light). I tried spray on Flex-Seal and self-adhesive felt panels. As the process progressed, you can see the reduction in reflections.

The Equatorial Mount came with no dovetail or rings, so I will be building my own. I put some flat stock aluminum through my roller as well. Some pieces will be the ring mounts, and some will be internal supports. To go from the flat plate to a curved ring, I cut blocks from a 3/8" flat stock with a scroll saw.

I 3D printed some knobs for 1/4-20 bolts, to connect through the bottom of the EQ plate to the arc blocks I cut. I drilled, tapped, and mounted the arc blocks. Then drilled and countersunk the rings. I then added some gaffer tape to the inside of the rings to increase friction and reduce scratching the tube. Some strap clamps were added to the ends of the rings to secure the tube. This completes the EQ Mount portion.

Knowing my woes from previously creating an 18-point mirror cell, I knew this one would be much less complex. Standard PLOP to get the best support points.

Using some flat bar, I drilled and used bearings from old hard drives. Some furniture magic sliders were attached as the mounting points (sliders to allow movement). Some 1/2 U-channel aluminum for the base. All drilled, tapped, bearings installed, and sliders mounted. I then cut some of the 3/8" stock for the corner pieces to join the U-channel together.

I created some retainer clips for the mirror, and added some self-adhesive Teflon tape to allow the mirror to move. Some wider and thinner aluminum flat stock was sandwiched between ring layers to provide a base for the triangle to mount to. Two screws at each point are spring loaded, one for collimation adjustment and one to lock it after collimation. Installing the mirror cell to the tube is done with some screws from the outside of the tube into the support rings. Installing the secondary/spider/focuser is done with screws from outside of the tube into the PVC ring of that assembly.

First light from the living room, through the window into the yard, allowed me to make some adjustments on the mirror placement. I then built a solar filter and took a shot of the sun (some focal work required). I took it out at night to complete a shot of the moon.

Then I packed it up and traveled to the center of the path for the eclipse. I checked weather and confirmed clear skies for the next morning during the eclipse. At dawn, I setup the telescope with a Canon M1 mirror-less camera and videotaped the event with this telescope. I also setup two additional cameras aimed at the sun with different focal length lenses. A 4th camera with an 8mm fish-eye lens to catch all the way to the horizon was not a good idea for a solar eclipse, but this method works better for lunar eclipses.

Overall a great experience with a lighter, portable telescope.