Lost and Found
Yesterday evening I happened upon my little Ricoh GX100. I thought I had lost it (perhaps on my most recent trip to the mountain), was somewhat distressed, and had even gotten as far as pricing some new models on the net. But it turns out I had just put it in a strange place. Very glad to have it back.
These are a couple of pictures that I had taken with the camera just prior to misplacing it. This is Subaru Telescope’s large 8.2 meter mirror, pulled off the telescope and stripped of the aluminum coating. It was awaiting aluminization (recoating). This is done approximately every 2-3 years and takes about two to three weeks. See the person on the far side for scale. This mirror blank took seven years to manufacture. The reason it took so long is the precise tolerances that Subaru demanded.
A map of the surface error of the mirror shows that the average bump is only 0.012 μm, or about one in five thousandths of the thickness of a human hair. If the primary mirror were the size of the Big Island of Hawaii, the average bump would only have a thickness of an ordinary sheet of paper.
The Big Island is 4000 square miles, a little bigger than the state of Connecticut! You can read more interesting details about the mirror here.