In message <[log in to unmask]> [log in to unmask] writes: > > So I'm kicking the question back to the film list. Can anyone answer this > for me? Why do wheels, when filmed, sometimes look as if they are > spinning in a direction which appears to be the opposite of the direction > which logic tells us they actually must be spinning? Does persistence of > vision have anything to do with it? Well as with all film, persistence of vision is all of it! The answer is quite simple, really...no doubt I will make a hash of explaining it. The speed of the camera frames, and the speed of the wheel, have a very narrow 'mismatching' window. basically, the camera records the wheel slower (or faster) than the whell is turning, which means the wheel has turned more (or less) than a full cirlce for the frame speed. The eye references on wheel spokes, and as the camera is replaying the spokes in the 'wrong' order, the wheel appears to be moving backwards uniformally. persistance of vision supplies the eye with the information of where the spoke was last time, and it's 'moved' back', rather than forward, and thus the carriage wheels move back, whilst the carriage moves forward. The speed ratio is interesting, on some extended carriage scenes, you can watch the wheels go foraward, slow, stop for a moment, and then roll back, although such shots rarely get through to final cuts. > > Does anyone have a good sound bite about this which they are willing to > share? Or at least can someone explain that wheel thing in case I bump > into any more armed and dangerous, precocious first graders? > > Thanks-- > > Meryem Ersoz > University of Oregon Give them circles of paper, marked with spokes, and flag one spoke a different colour. Then, they can fool around with frame speed, through piece of paper with a square hole cut in it! > > ---- > To signoff SCREEN-L, e-mail [log in to unmask] and put SIGNOFF SCREEN-L > in the message. Problems? Contact [log in to unmask] > -- Morgan "Nunc demum intellego," dixit Winnie ille Pu. "Stultus et delusus fui," dixit "et ursus sine ullo cerebro sum." ---- To signoff SCREEN-L, e-mail [log in to unmask] and put SIGNOFF SCREEN-L in the message. Problems? Contact [log in to unmask]