On Thu, Aug 26, 2010 at 6:06 PM, Speaker To-Dirt <[email protected]> wrote: > > Yes simple rigs can give you a sphere, nature gives that one to us. You can > do it by hand up to a meter or so in diameter. It took a few decades to > develop optical tests and parabolizing strokes to take the sphere and grind > it to a parabola, and nowdays, secondaries can be hyperbolas. A sphere does > not make a good imager unless the focal length is huge compared to the > diameter of the mirror. It's why old telescopes are long. But then f5 and > greater system are still parabolic primaries. I don't think you can go > spherical only until you start playing with f10 or greater. you could use a > Dall Kirkam, but you need some image field correction still. > > The machine tools used in mirror grinding are not encoded to twice the > limit required on the glass as called for by Mr Nyquist. All the optical > grinders I've worked with are close to run open loop along these lines. There > is a model by which glass is removed. Foccult testing and Hartmann testing > give you the high and low points on a mirror. Strokes with a given grit are > computed to remove the high surfaces, and then run on a machine that may only > be encoded to 0.010 inches/tick. You run the stroke, then run another optical > test, then compute another stroke ..... You keep going until the error is > within acceptable limits. Here's the machines I worked on. > > http://mirrorlab.as.arizona.edu/
So that's how it works! thanks for the explanation. That's pretty subtle. In the brute force school I know there are machines that directly cut optical surfaces with diamond tools. Yes, they are accurate to 0.1 um or so. ------------------------------------------------------------------------------ Sell apps to millions through the Intel(R) Atom(Tm) Developer Program Be part of this innovative community and reach millions of netbook users worldwide. Take advantage of special opportunities to increase revenue and speed time-to-market. Join now, and jumpstart your future. http://p.sf.net/sfu/intel-atom-d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
