Saturday, May 26, 2012

My School

Exiting development at work lately. Some weeks ago, I asked my supervisor if I can give lectures because I want to learn how to teach. It's part of J's five step plan. My supervisor asked me to give a series of introduction lectures for the new students in our research group. 
Teaching students at University level changed my life: My goatee transformed into a professor beard. and I become more serious. That's why I am not going to write an amusing story here. Instead I am going to lecture you - nothing funny about that.
My lecture today will be about the polarization of light. Electromagnetic waves like light are perpendicular or transverse waves. Transverse wave is a science-y term for a wave in which the oscillation is not in the direction of the wave propagation. It's like a wave created with a rope where each part of the rope moves up and down while the wave moves horizontal. Another common wave type is a longitudinal wave where the oscillation is in direction of the wave propagation like a queue, where everyone is pushed for- and backward by the closest persons and everybody holds position - a typical queue.
In 3 dimension transverse waves can oscillate in a bunch of directions. Light from light sources like sun, incandescent light bulbs, CFL, and others consists of waves oscillating in all directions. It is possible to filter some of these directions out so that the light has oscillation in one direction by using a polarization filter. If non polarized light (light that oscillates in all directions) got reflected on a non metallic surface with a certain angle part of the waves would become longitudinal waves. But, since light can not be a longitudinal wave, reflection of light on non metallic surfaces can make light polarized. So, what would happen if we would use a polarization filter on light that got reflected? We can either eliminate the reflection or enhance the reflection by reducing all the other light.
One field of application of polarization filters is photography. In the following pictures you can see how a polarization filter can change the green of leaves (by eliminating glare) and the blue of the skies (The color of the sky is basically a reflection).  With that we get an increase of the contrast between sky and clouds - clouds look fluffier.
No polarization filter @ISO 80, F4, 1/500 s
Polarization filter: decreased contrast between sky and clouds @ ISO 80, F3.2, 1/400 s

Polarization filter: Higher contrast between sky and clouds and different colors @ ISO 80, F3.2, 1/400 s
 The polarization filter will change also the mod of pictures from rainy days as shown in the next pictures.
No polarization filter @ ISO 80, F 2.8, 1/160 s

Polarization filter: enhanced glare @ ISO 125, F2.8, 1/80 s

Polarization filter: eliminated glare (note the road marking and the roof color)

 In the next picture you see why stalker love polarization filters.
Left no polarization filter; center polarization filter is enhancing reflection; right polarization filter is eliminating reflection

But polarization filters not only have an influence on reflections as one can see on my face in the next pictures.
No polarization filter... well actually you can see the filter... photo taken without polarization filter... without the use of a polarization filter
Polarization filter: Enhancing the smile

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