How did Galileo grind his lenses?

August 19, 2020 3:25 PM

How did Galileo hand-grind lenses for his telescopes? What did he do to maintain an even curvature? Did he just do it by eye?
posted by musofire to Science & Nature (5 answers total)

Best answer: Not a historian but probably relevant link
posted by GCU Sweet and Full of Grace at 3:41 PM on August 19, 2020 [1 favorite]

Best answer: This article addresses the methods used by Ippolito Francini, Galileo's Florentine lens-maker.
posted by niicholas at 3:42 PM on August 19, 2020 [11 favorites]

It probably does not reflect what Galileo did, but I ground an eight-inch mirror for a reflecting telescope and it shaped itself almost automatically. Using two similar-sized circles of thick glass, one fixed with pitch to lie on a board and the other rubbed over that in a randomized back-and-forth motion, with grit between them, resulted in the upper part getting a parabolic depression - i.e. exactly the shape needed.

In the end I hit a problem with the construction and the mirror didn't get completed, but it was amazing how it shaped itself so perfectly without special effort.

(On review, niicolas's link is much more useful; and my effort was thanks to meeting John Dobson, pointed to by GCU Sweet and Full of Grace)
posted by anadem at 7:59 PM on August 19, 2020 [2 favorites]

Very related, I highly recommend this book/long article, which dives deep into lens grinding tools:
Descartes and the Hyperbolic Quest: Lens Making Machines and Their Significance in the Seventeenth Century

Last I checked, it was free to read on google books here.
posted by Dmenet at 7:49 AM on August 20, 2020

So here's a website describing in extreme detail the making of a replica of his telescope. The section on actually making the lenses is not as detailed, but they have a picture of a lense grinding machine. Not sure if the machine itself has historical relevance, since it looks like it has an electrical motor, but I think some kind of hand powered version would have been doable at the time. They also have a section on testing the lenses, plus a lot about the specific shapes.
posted by anaelith at 5:19 PM on August 21, 2020