Circular Vs. Linear Polarisers
There are 2 types of Pol filter and to be honest i don’t know the difference in them other than what I’ve read. Linear polarisers are more effective and less expensive than circular ones but AF and metering in camera may not work as well with Linear and therefore camera manufacturers recommend circular. I only have a circular and never used a linear so I can’t say either way.
The results are there to be seen.
They allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also enable colours to become more saturated and appear clearer, with better contrast. This effect is often used to increase the contrast and saturation in blue skies and white clouds.
Now this is a geeky as it gets :). We know that our pol filter only lets light waves travelling in one direction through (kind of like putting coins into a slot, you just can put the coin in sideways with out breaking something). Cross polarisation is when we use 2 pol filter that are set at 90 degrees to each other. In theory no light should get through of course, no polarised filter is perfect, so some light will always get through, but the vast bulk of light is filtered out.
One way to do this is to place a polarised filter on your light source and one on your lens. the subject should be clear plastic. Due to the processes used in manufacturing injection-moulded clear plastics, the plastic has some ability to polarise the light itself. When the polarised light (from the light source) passes through these plastics, their phase gets altered. By filtering out all other light with the second polariser (on camera), your resulting image should look something like this ….
Notes About Polarising Filters
Here are a few other things to keep in mind when using polarising filters:
- When stacking filters, the polariser should always be the last (outermost) filter on the stack. Passing through a polarising filter further down the chain may alter the results of other filters you had used.
- Lenses with rotating front elements will mess up your polarising filter’s rotation. If your lens has a rotating front element, you should adjust the polarising filter after you’ve set the focus.
- The effect of polarisation (outdoors) is most prominent at a 90-degree angle to the sun.
- The angle of polarisation varies continuously with the angle from the sun. With a lens wider than about 28mm (in 35mm film terms) the sky will be unevenly polarised. If you like the effect, go ahead and use it.
- Reducing haze. Since light comes from all over at random polarisations, adding a polarising filter will block the crossing polarisation patterns of scattered and reflected light to reduce haze.
- Removing reflections. As mentioned above, light is naturally polarised when it is reflected, so by rotating your polarising filter to cross-polarise the reflected light, you can effectively remove reflections from the photo.
- Increasing colour saturation. By reducing haze from scattered, random light, saturation of colour is dramatically improved. The effect is particularly evident in skies and in foliage.
- Neutral density. The natural loss of 1-2 stops of light, without shifting colour, makes a polarising filter a good ND filter as well.