Saturday, June 9, 2012 5:15:47 PM
@MacGuffin, did you submit this ages ago? I recall seeing it in the Live Subs or something.
Anyhow, the explaination is simple, if counter-intuative. The "filter" doesn't block all the light, but most of it, and the rest is "oriented" a certain way. The second filter blocks those oriented that way. BUT when you put a 3rd filter in the middle, the orientation is changed! Now the 2rd (closest to the camera) filter lets most of the light pass through it!