4x4 polarizer, linear or circular? does it matter?

[antcuc]

Hi guys,
I'm looking for a 4x4 polarizer for my mattebox and the person selling theirs says the polarizer needs to be rotated to be used correctly.

I shoot with a t3i and 5dmii and have read that circular polarizers are best used with these cameras. Is that correct?

My other question is, which polarizer needs to be rotated, linear or circular? Or both? The seller has no idea which one he has and I'm trying to figure it out.

Thanks for your time.

[Ken Hull]

If the light goes directly from lens to sensor, without going through a prism, then it doesn't matter. They will behave the same. Circular polarizers were developed to accommodate cameras having a beam-splitter prism in the light path. A 3-CCD camcorder would have prisms to send the light to 3 different CCDs. Prisms tend to do some polarizing of their own, and that, combined with the polarization done by the filter, can confuse things. So each of the RED, GREEN, and BLUE sensors would get light polarized in different amounts. A DSLR shouldn't have a problem, although some people say that JUDGING the polarizing effect through the viewfinder would be problematic, because the light is bounced off a mirror and then sent through a pentaprism before reaching your eye. Hmmm.... well, maybe.

In any case, using a circular polarizer will work with any camera. A circular polarizer is a regular (linear) polarizer with a depolarizing filter added to the backside. So the light entering the filter is oscillating in 2 dimmentions (up-down, and side-to-side); then the image gets changed while passing through the polarizer by allowing oscillation in only one dimmension (you control what dimmension by how you rotate the filter). The result might be to turn the sky a darker, richer blue, if that's how you adjusted the polarizer. This changed image has the lightwaves oscillating in only one dimmension (the result of polarization). Then the light goes through the depolarizing part of the circular filter, which spreads out the oscillation in 2 dimmensions. It's OK, you don't lose the darker richer sky, or whatever effect you were after. The depolarizer just "spreads out" the light of the polarized image to be "circular" again.

From the Tiffen website:
A Circular Polarizer has the same effect as a Polarizer and is used on cameras with beam splitting metering systems commonly found on auto focus SLR's (for most 35mm auto-focus cameras see your camera manual).
Area of sky most effectively polarized with a Circular Polarizer:
Point your index finger at the sun. With your thumb extended at a right angle (90°), rotate it around the axis of the index finger. It will point out the band of deepest blue from horizon to horizon.

-- Ken

[antcuc]

Thanks for your in depth answer Ken I appreciate it. I have a better understanding and your point about a circular working with any camera is my deciding factor. Thank you!

[Ken Hull]

Oh, one more thing....
Since you're talking about rectangular filters for a mattebox, be sure the polarizing side of the filter faces the subject. If the depolarizing side were to face the subject, you wouldn't see any polarizing effect! My Schneider filter has the words "This side out" printed is small letters along the edge of one side. But it's easy enough to check: Just hold the filter up to your eye while looking at a specular reflection (off of a non-metallic surface). If you can rotate the filter to reduce the reflections, it's aimed correctly.

-- Ken

[antcuc]

Oh, one more thing....
Since you're talking about rectangular filters for a mattebox, be sure the polarizing side of the filter faces the subject. If the depolarizing side were to face the subject, you wouldn't see any polarizing effect! My Schneider filter has the words "This side out" printed is small letters along the edge of one side. But it's easy enough to check: Just hold the filter up to your eye while looking at a specular reflection (off of a non-metallic surface). If you can rotate the filter to reduce the reflections, it's aimed correctly.

-- Ken

Again great information Ken you're awesome! Thanks!

[Mitch Gross]

This might be helpful.

http://blog.abelcine.com/2010/01/25/...ons-explained/

[hscully]

Oh, one more thing....
Since you're talking about rectangular filters for a mattebox, be sure the polarizing side of the filter faces the subject. If the depolarizing side were to face the subject, you wouldn't see any polarizing effect! My Schneider filter has the words "This side out" printed is small letters along the edge of one side. But it's easy enough to check: Just hold the filter up to your eye while looking at a specular reflection (off of a non-metallic surface). If you can rotate the filter to reduce the reflections, it's aimed correctly.

-- Ken

I just picked up a 4 X 4 Tiffen polarizer, WTR/WHT Linear ultra pol. It is amazing on glare. I just did a test and when I rotate it in the matte box, I cannot tell a difference when I face it either way. I can have the writing going facing me or facing out and I get the same results.

Anybody know which way is right with this polarizer? I'm thinking writing facing "out" but really I can't tell a difference. Does it have to do with this type of poloarizer? I can post the test.