Quote:
Originally Posted by OzEclipse
Hi Logan,
Good on you. I made my own mirror for my first scope when I was 15.
While you are grinding the easy way is to swish some water over the ground surface and focus the sun. I had a long wooden stick 2m long. I attached a piece of white card to one end and marked distance at the other end. You can use 100mm markers for the longer lengths then drop down to 10mm markers near your target focal length. Take the mirror outside on a sunny day, slosh water over the surface and focus the sun on the white card, read the focal length off your distance markers.
A 10" f6 has a 2.6mm deep sagitta or curve. If you don't have the sun, you can lay a straight edge across the whole diameter of the mirror. Then compare the centre depth to a depth marker like a 2.5mm drill.
You only use these methods when you are rough grinding. Get the focal length a couple of inches longer than you want by the end of the 80 grit grind. The fine grind will take the rest off. By the time you get to Ronchi or Foucault test (not Focault) you are polishing and the focal length won't change much during polishing. You can however use these tests to determine the focal length accurately.
Have fun mate.
Joe
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Thanks for that Joe!
I will definitely be using these techniques!
Quote:
Originally Posted by Baza
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Thanks Barry!
