[Sca-cooks] Farsighted lenses

[TerryDecker]

To the first question, it's why I want to read the book by Ilardi.  It's an 
American Philosophical Society monograph and they are usually very complete.

Once you have high quality glass (which the Venetians were doing in the 15th 
Century), the problem is not carving the lenses, it's making them conform, 
however roughly, to the problems of the eye.  Magnifying glasses are fairly 
simple to make (which is why reading glasses are cheap and OTC) reasonably 
accurate corrective lenses aren't.  I would think this would have been a 
trial and error process with a lot of rules of thumb, but it's worth noting 
Newton describes the optical properties of lenses in the 17th Century.

Bear

-----Original Message----- 

This is the first I've heard of concave lenses within our period, at all. 
Like Urtatim, this comes as a surprise to me. Interesting, but I think I'll 
hold it with a bit of skepticism until I see some more supporting evidence. 
Bear? Seen or heard of these letters?

I don't see that it is that more difficult to carve concave lenses if you 
can do convex ones. You mainly need the idea and reason to do so. Getting 
the clear, consistent  glass is the biggest problem.

Stefan