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Unable to find image IMG_20240417_000708615_1.jpg Unable to find image 20240416_233201_124816.jpg 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!
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So I was talking to new local friends and telling them about telescopes and someone says “I have a mirror sitting on my table, is that something that could be useful?” and so after picking it up I now have a ginormous 12.25" mirror that’s 2.25" thick!!
…now what do I do with it? Honestly I’m tempted to make a scope out of it… but that would take money and I’d need to learn new skills like woodworking.
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Introducing “Finley”, probably the jankiest and most colorful eclipse imaging setup of all time. The only telescope I have which is enclosed (and therefore safe to use on the sun) is this donated finderscope, meaning I’ll have crosshairs in all my images. I’m taking pictures using my friend’s phone which he gave to me after the screen cracked. I designed a 3D printed adapter so it fits on the sturdy 3D printed mount I designed for the far bigger Hadley telescope.
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I finally saw my friend’s kiln! It’s a big kiln.
I took the cement mold (the wrongly shaped one) and cast it into the flames for displeasing me.
Looks like the kiln can successfully get up to 1200 degrees F! The problem is, the kiln controller can only go up to one target temperature. For the actual glass slumping, I will need a ramp/soak controller, which can let me program it to hold at a certain temperature for some amount of time then move onto another temperature.
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…the cement form’s curvature isn’t right. I measured the sagitta (how deep the curve is in the middle compared to the edge) and it’s 1/16". it should be around 1/4". This would make a telescope that’s 12 feet long.
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAARGH
I CNCed mold’s shape wrong. I have two choices: I can either grind/sand down the edges of my cement form into a deeper curve (probably releasing tons of bad to breathe in dust), or start the process all over again with new wood.
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In addition to grinding an 8" mirror, I’m trying a technique to make big thin 12" mirrors. See the #meniscusmirror tag for more. Previously, setting things on fire didn’t improve the problem.
Now I have a $35 tub of castable furnace cement (amazon had it for $14 cheaper than home depot). It’s dry sand that needs water and throws up clouds of dust, glad I have a respirator from covid.
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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.
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Unable to find image 512image2.png Unable to find image 512image.png 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!
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