Quote Originally Posted by ic-racer View Post
Edmund optics carries heat absorbing glass in various sizes. 51mm x 51mm is $13
You mean the Schott KG Glass types listed here as heat absorbing glass?:

http://www.edmundoptics.com/onlineca...productID=1934

One thing that is a little bit confusing is that Schott seems to make 4 grades of heat absorbing glass (KG1,2,3 and KG5). Looking at the transmission graphs, it seems the lower the number, the higher the transmission, but also the wider the transmission curve and the further it extends in the direction of near infrared.

kg1.gif

kg2.gif

kg3.gif

kg5.gif

From http://www.optical-filters.com/heatabsorbing.html

And this graph from the Schott glass webpage:

Schott_KG_Glass.JPG