Wayne Kinney asked me that just a few days ago, so I'll quote myself:

<<<<Wayne, I can't tell much about the condensers, because I just took them from old lenses. One from the front lens of a telephoto and one from a super8 film camera zoomlens. Both are pretty weak and thin. Almost flat ,slightly concave on one side. I put them like this (|GG|)>>>>


They are not that good for the hotspot, so I zoom in a bit. But they increase the light and the image quality very much.

plcx lens placement
 

Hi Andy : great to hear about your 35 mm adapter.

You might want to try this: You have the two plcx lenses with the ground glass sanwiched in between. (l). This would put the perfect focal point between the 2 plcx lens, in the center of ground glass. I think if you placed a clear
piece of glass (the same thickness on top of the etched side), the focal point between the two plcx would be directly on the surface of the ground glass.
(ll)