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I’m parabolizing my telescope mirror - I’ve ground it to a sphere shape, and now I’m grinding a tiny bit more to change its shape precisely into a parabola.
I’ve done 3 grinding sessions for a total of 34 minutes of grinding. Here’s a Ronchi picture of my current progress. Mel’s online Ronchi calculator has overlaid some semi-transparent white lines which show the ideal Ronchi grid of a somewhat parabolized mirror.
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| 115 words
Unable to find image image.png Unable to find image texereau-normal I’m parabolizing my telescope mirror - I’ve ground it to a sphere shape, and now I’m grinding a tiny bit more to change its shape precisely into a parabola.
I’ve done 3 grinding sessions for a total of 34 minutes of grinding. Here’s a Ronchi picture of my current progress. Mel’s online Ronchi calculator has overlaid some semi-transparent white lines which show the ideal Ronchi grid of a somewhat parabolized mirror.
Read More
| 2 min
| 301 words
I’m in the home stretch - my goal is to turn this sphere shaped mirror into a parabola shaped mirror.
The final stage of mirror grinding is called either parabolizing, because you’re making a parabola, or figuring, because you have to measure carefully and that involves numbers which are also called figures. You use a stroke that goes up and down fast and side to side slowly in a big zigzag, called a W stroke, to remove a tiny bit of glass from both the center and the edge, as seen in the first picture (from Mel Bartels’ site).
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| 316 words
Unable to find image parabolastrats.png Unable to find image 510400-1.png Unable to find image 510400-2.png I’m in the home stretch - my goal is to turn this sphere shaped mirror into a parabola shaped mirror.
The final stage of mirror grinding is called either parabolizing, because you’re making a parabola, or figuring, because you have to measure carefully and that involves numbers which are also called figures. You use a stroke that goes up and down fast and side to side slowly in a big zigzag, called a W stroke, to remove a tiny bit of glass from both the center and the edge, as seen in the first picture (from Mel Bartels’ site).
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| 346 words
This site is my secret weapon: https://www.bbastrodesigns.com/ronchi.html
It’s a slightly janky javascript app made by some old telescope maker in Oregon, and it lets you get quantitative measurements from all those Ronchi pictures. Very important.
Looks like my outer zone focuses light at around 0.066 in from my desired radius of curvature, and inner zone focuses light at around 0.1 in. (There’s probably big error bars on both those numbers).
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| 361 words
Unable to find image 4995398-pic-1.png Unable to find image 4995398-pic-2.png Unable to find image texereauabberation.png This site is my secret weapon: https://www.bbastrodesigns.com/ronchi.html
It’s a slightly janky javascript app made by some old telescope maker in Oregon, and it lets you get quantitative measurements from all those Ronchi pictures. Very important.
Looks like my outer zone focuses light at around 0.066 in from my desired radius of curvature, and inner zone focuses light at around 0.
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I’M SO CLOSE TO A SPHERE
(You know you’re a sphere when the lines are completely straight. See this infographic for more)
total mirror grinding time: TWENTY GODDAMN HOURS
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Unable to find image IMG_20240309_162343854~2.jpg Unable to find image IMG_20240309_162149283~2.jpg Unable to find image IMG_20240309_161749437~2.jpg I’M SO CLOSE TO A SPHERE
(You know you’re a sphere when the lines are completely straight. See this infographic for more)
total mirror grinding time: TWENTY GODDAMN HOURS
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I did 20 minutes without my center paper cutout and managed to dig a tiny zone in the center. Yaaaaay. Then I spent two hours ignoring it and trying to get the outside zone down.
On the plus side that outer zone at 70%+ diameter looks spherical now.
Now I have a choice: I think I’m close to a parabola. With that deeper center, if I can flatten the inner edge of that transition I’m very close.
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Unable to find image image-6~2.png Unable to find image image-5~2.png I did 20 minutes without my center paper cutout and managed to dig a tiny zone in the center. Yaaaaay. Then I spent two hours ignoring it and trying to get the outside zone down.
On the plus side that outer zone at 70%+ diameter looks spherical now.
Now I have a choice: I think I’m close to a parabola.
Read More