Help with Circular Polirizer Filter

andygazio

Member
Friends,

Sounds crazy, but I'm having trouble with a Circular Polirizer Filter. Actually it is the 3rd one the manufactor sent me. And they all seems not to work properly.
When I mout it to my camera (Sony PDW-F800 / XDCAM 422), if I rotate it, I get only a little change in color. But when I hold it in front of my lenses inverted, with the screw outside, I get exactly what I would expect from a Polirizer filter.
I've learned that a good way to test a CPF is to put it in front of a LCD TV or display. The LCD emits polirized light, usually in 45 degres. So the filter would affect how you see the LCD.
I did ecxactly that and I got a little color change when placing it correctly in front of the LCD. But I got what I expected when I holded it inverted.
Took some pictures...
I assumed it was mounted inverted in the manufacturing process. But 3 of them?
Any ideas?

Thank you very much for your help!



 
Last edited:

Shootblue

Well-known member
I used to know the answer and have forgotten...I must be getting old. I do know B+W are expensive but great.
 

Run&Gun

Well-known member
Also... You shouldn't need a circular polarizer on a broadcast camera/manual focus lens. You should only have to buy a circular if you're using it on a DSLR or something with thru-the-lens auto-focus and metering.
 

Douglas

Well-known member
Run & Gun, that is not true. Some video cameras do require circular polarizers.

Back in 2009 I noticed color-shifting problems whenever I used either of my two linear polarizes on my EX1 and EX3. But there was no color shifting when using a circular polarizer. So, I wrote to Tiffen to report the problem because they were the manufacturer of one of the filters. And at that time they were publicly saying that anyone who saw a color shift was mistaken. Well, I wasn't mistaken. I could see it happening right on my vectorscope so it wasn't even open for opinion.

This is the one of the replies I got back from them in 2009:

Quote:

[FONT=Calibri, Verdana, Helvetica, Arial]"I decided to head back to the lab (and my optical engineers) and take a good look at this issue. It has become apparent to me through spectral tests as well as general theory that the following is happening. All beam splitting prisms in all video cameras create some level of polarization of the light that is reflected from the prisms. Generally this is extremely minimal and therefore not an issue. A linear polarizer will cross polarize with any other polarized light such as the light reflected from a prism in a video camera. This could cause color shift (either warmer or cooler) because the red and blue channel are polarized while the green channel is not. A circular polarizer will not cause this problem because it does not create the cross polarization. If the color shift is only at the edges of the frame then there is a phenomenon known as "color shading" that is occuring and this is another kettle of fish altogether which requires further image analysis to discover the cause.

The Sony EX1 and EX3 obviously have some greater level of polarization reflected off of the beam spliter and therefore causing cross polarization of the blue and red channels. I have maintained for sometime now that virtually all video cameras do not have this greater level of polarization off of the beam splitter and therefore a linear will work just fine. We can now modify that to say that there may be a few out there that polarize more than others and therefore a circular polarizer should be used. As I have always said, if you want to be safe use a circular but you most likely will not need it; unless you own a Sony EX camera."

end quote.

[/FONT]
I have not bothered to test any of the newer cameras, such as the PMW-200 or F3, but I would be really surprised if they did not show the exact same problems.
 

Run&Gun

Well-known member
Good information Doug. I was going off of information that I had and had researched years ago when I was curious about the difference between linear and circular polarizers. The quote reads like you don't really need to worry about(or will notice) the phenomenon on "bigger cameras", but I guess anything is possible. I have linear polarizers for my big cameras and I've never noticed a "color shift" under normal conditions, BUT depending on the brand of polarizer there can be a noticeable color shift when shooting through polarized film http://www.rosco.com/FTVP/roscoview.cfm (making variable ND for windows).
 

Ben Longden

Well-known member
Ive always been confused about circular polarisation, as I have linear ones... the rope and gate analogy... but I have tried a circular one on the big camera, and it was pretty awful compared to the linear one. Thanks for sharing that one.
 

BluesCam

Well-known member
I noticed a huge color shift toward green with an EX1 and a linear polarizer. Some people thought I was dreaming. I'm glad I'm not the only one who saw it.
 
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