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How Do Linear Polarisers Work?


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#1 SuperbVision

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Posted 05 October 2005 - 10:07 AM

I currently have a circular polariser for my Canon EOS 300D though am considering investing in a 'Lee Filter' Linear Polariser.

At present I turn my circular polariser to achieve two different effects. How does a Linear Polariser achieve these effects? I assume you don't turn it around.

Are Linear polarisers better than Circular polarisers?

All comments will be greatly appreciated! Luke. wink.gif

#2 markgoldstein

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Posted 05 October 2005 - 04:26 PM

As far as I know you can't use a linear polarizer on an auto-focus lens - I can't remember the exact scientific reasons why. You need to buy a circular polarizer.
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#3 SuperbVision

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Posted 05 October 2005 - 05:19 PM

Thanks Mark, 'Lee Filters' also do a circular polariser, I will opt for that one. Just out of interest, if I use the manual focus override, would that then be compatible with a linear filter.

#4 markgoldstein

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Posted 06 October 2005 - 08:55 AM

No, you would still use a circular polarizer.

Here's what Luminous Landscape have to say:

Circular Vs. Linear Polarizers

There are two types of polarizing filters available linear or circular. Linear polarizers are more effective and less expensive than circular ones. But circular polarizers are needed with just about any camera that has a through-the-lens metering system, or autofocus.

The reason for this is that both of these systems use semi-silvered mirrors to siphon off some of the light coming though the lens. If that light is linearly polarized it renders either the metering or the autofocus ineffective. This means that you're going to have to buy circular polarizers unless you're shooting with a pre-1970's camera, or a view camera.

http://www.luminous-...olarizers.shtml
Mark Goldstein
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#5 SuperbVision

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Posted 07 October 2005 - 08:25 AM

Many thanks, Mark.

This information is incredibly helpful.

Luke

#6 markgoldstein

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Posted 07 October 2005 - 08:27 AM

No problem - that's what I'm here for!

QUOTE (SuperbVision @ Oct 7 2005, 08:25 AM)
Many thanks, Mark.

This information is incredibly helpful.

Luke

Mark Goldstein
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#7 eltel22

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Posted 13 October 2005 - 12:30 PM

I have a circular polariser, and you have to remember where the optimum point is. On mine, which I bought from Jessops, so long as you have the word "Polariser" at the top, you get good results. But it is only for bright light, where there is a lot of glare. But it cuts out about half the light available, so it increases the length of exposure necessary, for a given aperture value. For less severe light conditions, I use a Skylight filter, which fits the same way. It is less drastic, and still protects the lens. Think of it as an optical condom.




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