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Best Polarizer for removing reflections


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#1 Mathew Rudenberg

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Posted 07 February 2009 - 02:58 PM

So, I have a show coming up with a lot of cars and reflections.

Are some polarizers better than others, or does it only depend on the angle you shoot from?

If they do differ what are you favourite makes/brands?

Also, what is the best angle to eliminate reflections from cars (I read 30 degrees between camera and surface, 30 degrees between surface and reflection)
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#2 Phil Rhodes

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Posted 07 February 2009 - 03:59 PM

In general, the effect of polarising filters is more or less consistent. Different grades and makes are distinguished mainly by the relative thickness of the microscopic lines that form the polarising array (palings), where the ratio between the width and spacing controls, to some extent, the intensity of the effect. I have seen different grades of filter behave differently in this manner, although I've never actually seen manufacturers offer a choice in the matter. Very cheap polarisers (and polarisers are expensive) can be so coarsely-made in this regard that they appear to directionally blur the image at an angle 90 degrees to the palings, but you'd have to buy a particularly nasty one for that to be an issue.

More specialist types involve the use of colour filter dyes for the palings, as opposed to an opaque black - these filters variably tint areas of the image in response to the degree of polarisation, although that's probably not what you want here and this is a special case. They were used on Planet of the Apes to selectively tint the sky of the supposedly alien world.

The major technical variability of polarising filters is the application of a quarter-wave retarding layer on the back surface, which has the effect of depolarising (or more correctly, circularly polarising) the light once it's been processed in the filter. These are referred to as "circular polarisers". This is done purely so as not to confuse the automatic focus systems in many DSLRs, which often use pellicle or semi-silvered beam splitters so that the sensors can see what the camera is looking at, which are sensitive to polarisation. The only difference this makes is that the thing doesn't work when it's the wrong way round, and you could possibly argue that the additional layer costs you some optical quality.

So in general, a pola is a pola. As to angles, go and look up Brewster Angle on Wikipedia.

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#3 Mathew Rudenberg

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Posted 08 February 2009 - 12:25 AM

excellent, thank you.
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#4 Jake Iesu

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Posted 21 February 2009 - 05:13 PM

Nice post, Very interesting, I wasn't aware of the focus problems with DSLR's Do you have a source where i can read more about science behind that?
On the topic of Pola's. Is their physically a difference between a "True Pola" and a standard Pola? or is it just a marketing thing used by schenider.
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