Got my new Camera, question about Polarized Filter

Here is a mini tutorial on light polarization.

The short answer to your question is No. Polarizers can darken the sky and remove glare off reflected light. They are particularly good for landscape and outdoor photography where the contrast between the subject and the sky might be very high. For example, the subject -- a mountain and the land facing it -- might be more dimly lit than the sky. A polarizer (i.e. a circular polarizer) can darken the sky without darkening the subject, thus reducing the contrast between these elements and allowing to you snap a picture that reveals details in the subject and in the sky.

Unlike UV filters, polarizers should not be left on all the time.

Dark said:

Anyhoo i have a question, in the accesories i got, i got a polarizer filter. Now I was reading up and they say for Auto-Focous its like a neccesity.

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You've misunderstood what they're saying. There are two main types of polarisation: linear polarisation (which is what you get with sunglasses), and circular polarisation. (No, I don't fully understand the difference myself. Anyway.)

If you have autofocus on your camera -- and I'm pretty sure all modern cameras do -- then you need to get a circular polarising filter if you want to keep the ability to autofocus whilst using the polarising filter. A linear polarising filter stops autofocus from working properly. It is not, as has been mentioned, necessary or even advisable to keep the polarising filter on all the time; it's mostly useful for outdoor shots, in fairly bright conditions.

So in short: for general shooting, the polarising filter is not necessary. When you want to use the polarising filter, make sure it's a circular polarising filter (which most sold nowadays will be), and everything will be happy.

Circular polarisers........I can't remember how they work from taking optics at Uni, but I would have thought that they would block out pretty much all light.....

And what makes light from the sky different from light reflected from objects (eg: trees and mountains)?? Is light that's reflected become circularly polarized, which means that light coming from the sky isn't, and so the sky appears less bright?

Circular polarizers will suppress glare and enrich colors. However, they also act like neutral density filters, which reduce the amount of light passing through without affecting any other properties.

At high elevations such as Yosemite or Tahoe in the Sierra Nevadas, or the Colorado Rockies, circular polarizers are almost mandatory for capturing beautifully rich and detailed pictures. They are also a must-have for seaside and lakeside pictures.

Abstract said:

Circular polarisers........I can't remember how they work from taking optics at Uni, but I would have thought that they would block out pretty much all light.....

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Wikipedia has some useful information. In short: light travels in a given direction, and has wave-like "vibrations" in the plane perpendicular to that same direction. (Perpendicular meaning that the angle between the direction of travel and that plane is 90 degrees, no matter how you measure it.) If those vibrations are strictly in one direction (so it traces a line from one end to the other), the light is linearly polarised.

If the vibrations are circular, on the other hand -- so the vibrations are such that they would form a circle on a sheet of paper if you could see them -- they are polarised as by a circular polariser. It's a different form of polarisation, but it is polarisation nonetheless. You're confusing circular polarisation with putting two linear polarisers together, at 90 degrees to each other -- which would block most of the light, as you say.

I don't pretend to understand what happens to light when it bounces off a given surface, so I'm not about to try to deal with the rest of your query.

None of this is really necessary to understand for the purpose of photography, but it's interesting nonetheless (at least to me )