In this episode:
History and terminology: Fresnel lenses
Here's a diagram for your enjoyment: http://www.uq.edu.au/_School_Science_Lessons/188.8.131.52.GIF
The New York Times re-instates designer credits
Tech talk: plots
Note: you will notice that my voice changes dramatically about halfway throughout the episode. This is due to my recording most of this show on location at a gig.