Quote - ...my magnifying glass should only magnify... not de-magnify, whichever side of the lens I look though, he he...

Indeed it will.

Practical magnifying glasses are often made with assymetrical curvatures, which I seem to remember is something to do with reducing chromatic aberration. No need to worry about that, though; Firefly is nowhere near an accurate enough light simulator to have that problem.

On the other hand... Your magnifying glass effect might be enhanced if there was some visible aberration. I have no idea how to achieve that in the renderer, though, or even if it is possible at all; I suspect not. Postwork may be required. ;)