| 1 min
| 41 words
8" telescope: COMPLETE!!
It has literally taken all year, but my second telescope ever is done! It’s made of 3D printed parts, metal tubes, nuts and bolts, and a mirror I hand-polished over the course of 8 months! I’m very proud.
| 1 min
| 160 words
Update: at long last, my now aluminized mirror is finally being shipped back to me!
A timeline of recent events:
October 19: The mirror is aluminized. The aluminizer notes that he will wait a week to ensure the coating cures properly (reasonable and expected)
November 1: I am told that the mirror is “all set to send it out”
November 7: I ask for any shipping updates
November 10: I get a reply saying “I’ll do it tomorrow”
Read More
| 1 min
| 54 words
My 8" mirror that I polished by hand is officially a mirror! The person with a vacuum chamber, who I gave my mirror to two months ago, finally aluminized my mirror and sent me a picture! It’s shiny and reflective like a mirror should be!
Now it just has to survive being shipped back…
| 1 min
| 165 words
My 8" mirror is done; now I need to aluminize it.
The final step of making a telescope mirror, after spending months grinding glass into a parabola, is to cover the perfectly shaped glass in a thin layer of shiny reflective metal.
The most common technique is melting aluminum in a vacuum chamber so the atoms gently float onto the glass and stick. (There’s also a newer spray silvering technique that involves $400 of chemicals but amortizes out to cheap for many mirrors.
Read More
| 1 min
| 146 words
Someone brought an extremely accurate “double pass autocollimator” tester to an amateur telescope maker meetup… and it showed an uniform shade of gray across the whole mirror, meaning no defects (ignore the circular reflections from the test stand). That means my mirror is an extremely smooth parabola! I’m done mirror grinding!
🎉 First mirror: complete! 🎉 That’s so cool! I thought I was slightly overparabolized based on my Foucalt testing.
Read More
| 1 min
| 197 words
I did a tiny bit more parabolizing, then re-measured my mirror. Last time, my spreadsheet and measurements told me my outer zone needed to focus tiny bit farther and my lower zone needed to be a tiny bit closer. To dig the inner zone out, I did some W strokes with lots of mirror movement on the tool edge, and then used long center over center strokes with a tiny offset to dig everywhere but a tiny strip of outside.
Read More
| 1 min
| 121 words
I’ve switched to using the Foucalt test and a Couder mask for parabolizing. The Foucalt test is more precise (but more annoying) than the Ronchi test, but my local astronomy club has a foucalt testing rig with a micrometer that lets me measure very precise details of where different regions of the mirror focus light, so it’s more accurately moveable than my handheld Ronchi tester. I built a cardboard “Couder mask” to block off regions of my mirror to see where the edge and center are focusing light to separately.
Read More
| 2 min
| 232 words
I’m at the final step of polishing a telescope mirror: turning a sphere shaped piece of glass into a parabola shaped piece of glass, called “figuring” or “parabolizing”. I messed up, twice, and since then I have been regrinding my glass back to a sphere for figuring attempt #3. Today, after several months, I finally have a spherical enough surface to start figuring attempt #3!
Here’s both a Ronchi test and a Foucalt test.
Read More
| 1 min
| 117 words
It’s been a while but I gave the 8" mirror some grinding. I’m on my way back to sphere, undoing parabolizing attempt #2. 30 minutes of grinding seems to have created some turned down edge and a hole in the middle. Great.
I put the mirror into the telescope, leaned it against a big crate again, and I was able to use it to see the moon! It’s amazing that even though I’m not done figuring, it’s smooth enough I can see things in space.
Read More
| 2 min
| 225 words
My local astronomy club has a foucalt tester, and today I tested that mirror after 30 seconds of parabolizing. It revealed a big turned down edge (yahoo…) and some slight zones in the center of the mirror. I knew those zones existed - heck, you can even see the slight non-sphericalness in the second image of my “close enough to spherical!” celebration - but the radius of curvature changes rapidly where one zone meets another instead of smoothly blending.
Read More