Tuesday, December 8, 2009

Setting the M4-M5 spacing

Now that we've shown that at least 2 of the numbers in the metrology report differ from what we find, we'd like to either be able to measure Everything ourselves, or just not have to rely on the values given.  We aren't able to make accurate enough measurements with the Faro to allow us to determine the conic constants & the radii of curvature of the mirrors so it was time to summon our Zemax Guru for another epic simulation exercise...

This pair of mirrors can be thought of as a convex lens so the simple lens equation relating object & image distances to focal length (1/u + 1/v = 1/f) can be used to measure the focal length of the system, which in turn gives the separation of the mirrors.  By stepping the pinhole along (to change the object distance) & finding the image with the wavefront camera each time (to get the corresponding image distance), we could produce curves to decide how to adjust M4's Z position to match the best theoretical spacing.  Sorted :)

Our latest clean room interloper looks an awful lot like the axial spacing plot...  It's a solifugid - not quite a spider as it belongs to a different arachnid order.  They run fast, chase your shadow & have a reputation for all sorts of bad behaviour - most of which is unfounded, but still - they are fairly creepy :{

Watch this space...  We'll be removing & washing M5 over the weekend - yes, Really!

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