Why Would Anyone Want to Do This?
Prior to the 2024 eclipse, I sold my telescope, opting for a standard DSLR with a telephoto lens. I lost a bit in clarity, as my lens maxes out at 300mm (the telescope had an effective focal length of 1350mm). There is one significant advantage, that I have now begun exploring. I've picked up a star tracker mount kit from the Czech Republic, allowing for deep-space imaging. Assembly is complete, but I then noticed a real problem. When I placed it on my telescope, it was horribly wobbly.
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| This image is a composite of two images, one where I'm pushing against
the lens (to the right) and one where I'm pulling it (to the left). |
Notwithstanding some error due to not being able to hold the camera steady, it gives some indication of the wobbliness. I lined the images up along the first joint atop the tripod legs. Note in particular how the amount of offset increases as you get farther away from the pivot point. While this pan/tilt assembly may be good for camera use, it's inability to support the weight of the tracker makes it a problem in this application. What I needed was something much simpler with fewer connection points. Step one is thus to remove the pan/tilt assembly from the vertical shaft. I just applied a little force while continuing to crank, and it came out with no damage at all.
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| The pan/tilt assembly is separated from the tripod. |
Thinking Through the Solution
My first thought was that I would use a threaded rod with a couple of bolts, but that I'd need to get one of the bolts welded to a plate that I don't have. No worry, I thought, I'm off work this week. I'll call a fabricator and have it done in minutes. So off to the city I go to pick up the parts. I picked up a 24" length of 3/8" threaded rod, a pack of bolts, a large washer... and that's when I saw it: a piece of 1/4" thick plate steel, 4"x12".
1/4" is thick enough that I could thread the plate itself, and screw the rod through it. Then, I could use the second bolt to tighten down against the plate, and no welding needed! Well, I just bought that thing right up and brought it home is what I did! I was amazed at how easily my reciprocating saw went right through the steel as I cut off a 4" square piece. I was worried that it was going to be a strenuous effort, but not at all. Drilling and tapping of the center hole were not any more difficult, though it was a bit of a chore keeping the drill bit and the tapping bit straight as I tapped the hole.
The Result
The 24" rod was more than I needed, so I cut approximately 4 inches off. As I expected, the second bolt under the plate provided enough security to lock the plate to the rod (which comes in real handy when trying to attach something to the threaded rod) without damaging the aluminum shaft.
I left just over 3/8" of the rod sticking through the top of the plate for mounting accessories to the tripod. I secured the bottom with a washer and another 3/8" bolt. It's tightened down to maybe only 3 or 4 pounds. It only needs to be tight enough to prevent slip during imaging. Tightening too much would damage the tripod's center shaft.
Here is the new configuration in action:
The image on the top shows the tripod being used for strictly the
camera. In this case, the ball-head mount can attach to the same
threaded rod. This means that with the pan and tilt capability of the
ball head, we no longer need the original pan/tilt assembly that came
with the tripod (less stuff to carry, and less stuff to fail). When using the star tracker, it spins smoothly down the threading and seems to hit the entire plate at the same time, confirming at least that I was close to being perpendicular with the drilling/tapping. Once secured to the surface of the steel plate, there is enough room for bubble levels on the edge of the plate to verify level.
The total cost was around $21.00 for materials, and about 30.00 for tools that I didn’t have:
Materials|
| Threaded rod | 3.00 |
| 4”x12” piece of ¼” plate steel | 16.00 |
| 3/8” bolts | 2.00 |
| Washer | 0.50 |
| 21.50 |
Tools
| 3/8” tap bit | 9.00 |
| 5/16” drill bit | 4.00 |
| Handheld tap driver | 15.00 |
| 28.00 |
Labor: About two hours
Yet to do:
- I'm considering putting bolts, or possibly pins in to hold the bubble levels in place (and of course, I need to get the bubble levels).
- I'd like to give the plate a good sanding, then hit it with a few coats of primer followed by a few coats of black. Bake that for about 15 minutes, and it will make a nice and durable finish. (But not in the oven you make food in. This process will ruin an oven, so better to use an old toaster oven that you can throw out.)
- I've given some thought to welding a small set of 'wings' on the bottom nut to allow for in-the-field tightening. If it came loose, this would be a faster and lighter way to re-tighten the nut.
