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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’m using an advanced technique: cutting out pieces of paper and putting them under the tool while pressing to avoid certain areas of the tool touching the mirror. I know I have a hole in the middle, so by blocking the middle from wearing down I can concentrate my wearing on the outer zones without making the center even deeper.
Looks like after a few hours I’ve managed to get the outer zone almost completely spherical!
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Unable to find image IMG_20240306_124746726_1.jpg Unable to find image IMG_20240306_160753289~2.jpg Unable to find image IMG_20240306_160449695~2.jpg I’m using an advanced technique: cutting out pieces of paper and putting them under the tool while pressing to avoid certain areas of the tool touching the mirror. I know I have a hole in the middle, so by blocking the middle from wearing down I can concentrate my wearing on the outer zones without making the center even deeper.
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Check out this infographic of how to read the Ronchi tests of my telescope mirror! I’ve been posting lots of pictures like this as I grind, and this tells you how to interpret what the pictures say about a mirror’s shape. The Ronchi test can be used to roughly measure a mirror’s shape and see any turned down edge (“TDE”), and with a computer program to analyze them, even give some quantitative measurements.
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Unable to find image ronchi_infographic.png Unable to find image 4890338-a-ronchi-test-infogr-image.png Check out this infographic of how to read the Ronchi tests of my telescope mirror! I’ve been posting lots of pictures like this as I grind, and this tells you how to interpret what the pictures say about a mirror’s shape. The Ronchi test can be used to roughly measure a mirror’s shape and see any turned down edge (“TDE”), and with a computer program to analyze them, even give some quantitative measurements.
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This pretty art piece is actually a precise measurement of my progress in telescope mirror grinding. It looked fun enough out of context I decided to post it!
You’re looking at multiple overlaid square images. Each one is a Ronchi test, which tells me the shape of my mirror on a nanometer scale in the shape of the red stripes. As I polish the mirror, it changes shape, so after 20 minutes of polishing I want to measure the new shape.
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Unable to find image ronchiart.png This pretty art piece is actually a precise measurement of my progress in telescope mirror grinding. It looked fun enough out of context I decided to post it!
You’re looking at multiple overlaid square images. Each one is a Ronchi test, which tells me the shape of my mirror on a nanometer scale in the shape of the red stripes. As I polish the mirror, it changes shape, so after 20 minutes of polishing I want to measure the new shape.
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To test the shape of a mirror, amateur telescope makers have a few tests which involve bouncing light off the mirror to see its shape. One cheap one is the Ronchi test, which sends light through a grating of fine lines, bounces off the mirror, and then you place the grating at the radius of convergence of your mirror so it blocks part of the light and reveals the mirror shape.
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Unable to find image IMG_20240126_215335157_1.jpg Unable to find image IMG_20240127_110757751.jpg Unable to find image IMG_20240130_005945275_1.jpg Unable to find image IMG_20240130_004837861.jpg To test the shape of a mirror, amateur telescope makers have a few tests which involve bouncing light off the mirror to see its shape. One cheap one is the Ronchi test, which sends light through a grating of fine lines, bounces off the mirror, and then you place the grating at the radius of convergence of your mirror so it blocks part of the light and reveals the mirror shape.
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To give a circle of glass (approximately) the right curve for a telescope mirro,, I want to make a precisely shaped mold that can withstand kiln temperatures. This technique makes what’s called a meniscus mirror.
Last time I tried this, the wood delaminated and came apart at the boundary where one plank was glued to another. This time, I’m spraying the wood with polyurethane spray on both the front AND back side, to avoid any warping before I put the furnace cement in.
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