I've been given a pair of polarized "3D movie" glasses to play with, but they've confused me.
If I put them on and look at my LCD (DELL E171FP ) monitor, the image on one eye is slightly different to the other. One's slightly browner, the other slightly greyer.
If I take the glasses off, and still looking from the "proper side" tilt them to and fro (clock/anti-clockwise) the effect is more pronounsed in both lenses...
I sort of expect that a bit, seeing as they're polarised and all
Now, the confusing bit. If I turn the glasses round (so the ear-hooks point towards the screen, and then repeat the to-and-fro motion the screen goes MUCH more dark (probably what I would have expected in the first place)... SO, how comes the lenses behave differently when viewing from one side to the other?
Edit.. it's a bit better than that... if I look though the lenses (backwards) and tilt my head left/right (anti-clock/clockwise) the whole display goes black with the neat exception of loads of little dust particles on the screen (it's a bit grubby, you see) - Really neat... I never knew it was sooo yuchy
ReplyDeleteYou've had enough of the mushrooms now, Andrew...Really, put your fork down...There's a good lad!
ReplyDeleteIf only you knew the truth...
ReplyDeleteLeave him alone - it keeps him off the streets.
I think the reverse thing is because it's probably a two-layer polariser, but I'm nowhere near good enough a physicist to explain it properly.
I expect that the reflection properties are not symmetrical. Like a half-silvered mirror... ?
ReplyDeleteAH, so a thin polarizing layer/film sprayed on one side (the outside) of the lens - when you look through the film first it has more effect (rather then through the diffusing action of the rest of the lens)
ReplyDeleteYes, I'd never thought of it like that.
ReplyDeleteNo not quite - I think some polaraisers (certainly those used in photography - possibly circular polarisers) have something like a quarter twist on one layer and a full 180 on the second, and for reasons I don't remember and more importantly, understand, don't appear the same depending on which side you look at them.
ReplyDeleteCan't remember the reason, but I know that a lot of autofocus cameras won't work correctly with a normal polariser, and need to have a circular polariser.
I'll have to go digging
[time passes]
Best I could find http://en.wikipedia.org/wiki/Photographic_filter#Polarizer
Probably a better one out there somewhere.
Wow!
ReplyDeleteMost polarisers are circular polarisers which work by sandwiching together two layers. The first is a linear polariser and the second is a half-step retardation place (which essentially makes the polarisation twist in a helix/spiral rather than an up-down/side-side linear polarisation. Let's call it a circuliser).
ReplyDeleteThe computer screen also acts as a linear polariser (apparently).
Two linear polarisers orientated at right angles to each other will block out (almost) all of the light. When you look through your glasses in the 'wrong' direction, that's what you're seeing. The fact that there's a circuliser on one end is neither here nor there.
If you look through your glasses in the 'correct' direction, the order is linear(screen), 'circuliser'(glasses), linear(glasses). The circuliser means that the light that goes through the second linear polariser is no longer polarised linearly itself, so will never be totally blocked (in fact it will be reduced by half).
Cameras use circular polarisation because they depend on internal mirrors - if a beam of light is passed through a linear polariser, then reflected back through the polariser, it will be blocked because the direction of polarisation has changed by 90 degrees due to reflection.
The colour difference you're seeing is a refraction effect caused because the polarising lenses you've got aren't quite perfect :)
Physicist strike!
I was just marveling at the fun that can be had with those things (free p. glasses)
ReplyDeleteLooking in a mirror and closing one eye shows the "other" eye's got an opaque lens
You could confound a kid with that!