Originally posted by stl
it works... but why does it works on LCD only? my CRT monitor cannot leh... i also tried on some HDB windows... those that i point towards has got no effect. But for those about 90 degree from my direction, it has got the changes when i turn the filter. Normally, does the filter works if i has to shoot through glasses/windows?
It works on LCD bcos LCD itself is made of Linear Polariser (means that the light from the LCD is already polarised!). And linear polariser confines light to a single plane, juz imagine that the light travel almost straight towards one direction. that is why sometime you cannot see clearly from the side of the LCD screen, unless you are in front of it. This is to suppress reflections and to eliminate glare.
A polarising filter works by only allowing light waves oscillating in a certain direction to pass though the filter.
When we rotate a circular polariser in front of the LCD, we are actually controling the light from a certain direction to pass thru the pl filter, and at certain point of the rotation, the ligth coming straigth towards the filter will be block or reduced, that is why you cannot see the light from the LCD since the light from the LCD is travelling straigth towards the filter.
We know that the light reflected from any surfaces is about 45 degree, that including glasses, window or a water surface. If you were to stand at 90 degree from the window reflection, you can actually see the reflected light and this will prevent you from seeing thru the window. Inorder to see thru, you need to block the reflection rite? so you need to use a polariser filter to block the light travelling from that direction.
That it! Enough of physic. Hope the explaination will help you understand more on PL filter. My explaination may not be clear but to understand in dept, you need to understand how light work at the molecular and photon level which I think will be quite boring
very chim lah..
If you still dun understand the theory, like ckiang has said...
turn until you like the effect!! that simple...
***Please take note that if you are using PL filter, you need to compensate for the lose of light by increasing the explosure by 1.5 to 2-stop
you can check out these sites for more info on polariser filter, it will give a better explanation to your questions.
http://photographytips.com/page.cfm/34
http://www.colorado.edu/physics/2000/polarization/index.html