On Feb 3, 12:03*pm, Yousuf Khan wrote:
On 30/01/2013 7:22 PM, RichA wrote:

The Kodak Ektamate and Ektar lenses all use thorium glass. *Pretty
harmless just sitting around but I wouldn't want to press my eye to
one for any length of time.

http://www.surplusshed.com/pages/item/l3759.html

What was the purpose of having a glass made of thorium? What was the
advantage?

* * * * Yousuf Khan

The heavier or more dense the glass the better, not to mention
offering a narrower bandpass that assisted the Kodak film to seem as
though offering a more visually identical result, instead of being
somewhat UV sensitive. Kodak film was already kinda IR tolerant by
simply not being sensitive to that longer wave spectrum because, even
deep reds (w/o special filters) didn't record all that well.