This depends on the focal length wanted. Once the sagitta is calculated, the coarse grinding can do. Using either a plaster effects or a glass object, the telescope maker grinds to approximately Eighty to Ninety percent of the sagitta required, rotating the glass while Rugged grinding. Once this operation is exhaustive, the workspace must be cleaned so that grit fibers don't dispose into the mirror.
Fine Grinding
Coarse Grinding
The antecedent effects that someone forging a telescope mirror does is grind a chamfer, or bevelled contour, all over the glass. Owing to any of manufacture a telescope mirror involves grinding a gap in the glass, the telescope maker must decide the Profundity of the gap, or sagitta.Succeeding, the telescope maker mixes the finer grit with hose and applies it to the grinding belongings. Instead of continuing to Muzzle into the gap, as with coarse grinding, the telescope maker grinds in a W shape, which makes the mirror amassed spherical. After grinding for a while, he inspects the mirror for vast pits, marking a rare of them with necromancy marker, which he Testament experiment to grind down. Searching for added pits, he shines an incandescent bulb on the mirror to gape how orange the display is. A properly ground mirror Testament panoply the alike Screen of orange across the surface of the mirror. When one grit vastness is done, the workspace and tools are cleaned again before Stirring to a finer grit. The task is repeated using finer and finer grits.
Polishing
Before beginning the polishing stage, the telescope maker yet again makes sure the workstation is completely clear of grit so that the mirror doesn't get scratched. He then places a container of pitch in a pan of boiling water to melt the pitch. The mirror and lap tool are placed in another container of boiling water. Once the mirror is heated, the telescope maker coats the mirror with a cerium oxide mix. When the pitch has cooled and has the consistency of molasses, he pours the pitch on the lap and places the mirror on top so that the mirror is completely covered by pitch. When the pitch has cooled, he begins polishing. Once the mirror is free from pits, it is measured to check that it is spherical and parabolic in shape using a Foucalt tester. When the mirror is complete, the telescope maker sends the mirror away for optical coating.
