So, after looking through about a dozen lighting books (mostly college texts) and even more websites, I still can't find a definitive explanation of PC lanterns - everyone has their own term that PC stands for, and the beam has been compared to both Fresnels and ellipsoidals, and it's a relatively uncommon instrument, at least here in the States... Can someone set the record straight? What exactly does "PC" stand for? (I've seen plano-convex and "pebble-convex" most) What is the beam and light quality like? How would one compare to a similarly sized Fresnel? Finally, aimed more to those outside the States, how common are they? Would it be worth getting a pair for our school auditorium (if nothing else, to learn about their distinct characteristics), or are they essentially relics from the past, not in common use? Thanks in advance, looking forward to learning more about them!