Hi All,

I've read the book Primitive Photography, and am thinking about trying to make my own duplet lens using a pair of identical achromats. Surplus shed sells lenses that might work but the achromat pair is separate crown glass and flint glass and not cemented. There is a comment on the page that says something like "don't worry we sell balsam too" but I'm not so sure about the idea of cementing the elements together myself and I don't know what "balsam" is or how it would help!

Right now this whole thing is just in the mulling over stage, but I'm curious to know if this is something to avoid.