Linear vs. Circular Polarizer

[Dan Keaton]

I have been attempting to research polarizers.

I want to purchase a polarizer, 4 x 4" or 4 x 5.65" for use with an XL H1 and a Chrosziel Mattebox.

From my research, it appears that a linear polarizer should not be used with a camera that has a beam splitter as part of its autofocus. Thus if a beam splitter is present, a circular polarizer should be used instead of a linear polarizer.

It appears that circular polarizers are generally recommended, as it is a safe recommendation in that in can be used with any camera.

However, a linear polarizer is technically better.

Has anyone used a linear polarizer with an XL H1?

Does anyone know if a beam splitter is present in an XL H1?

[Tony Davies-Patrick]

Circular PL filters should be used on almost ALL modern still cameras and DV movie cameras.

Even some older manual focus SLR film cameras, such as the Pentax LX, will not work with a regular Linear Polarizer filter and needs a Circular PL filter to work correctly with the advanced metering system (invented way back in 1980!).

Most modern DV camcorders will work OK with old Linear PL filters, but may cause some incorrect metering in some situations, so it is wise to just stick with the Circular Polarizer.

I have never seen any evidence or test results that show a Linear PL filter is any better than a Circular PL filter, so the main advice is to buy quality glass from the top marks such as B+W Pro, Hoya Pro line, Tiffen Pro line, Nikon, etc.

[Dan Keaton]

Dear Tony,

Thank you for the information and recommendation.

I was speaking with a true filter expert yesterday, one who has worked for three of the major filter manufacturers, and has worked as consultant for a major filter manufacturer.

The 1/4 wave retarder in the circular polarizer exacts a small penalty in performance. So I wanted to purchase a linear polarizer if at all possble.

I realize that even if the linear polarizer works for the XL H1, it most likely will not work for other cameras. Thus I consider the filter purchase a dedicated one-time purchase for the XL H1.

Since the XL H1 is a 3CCD camera, it must have a beam splitter to split the colors for each sensor.

What I wonder is:

Is the color beam splitter affected by a linear polarizer? I assume not.

Is this the beam splitter that filter makers refer to, or is there a separate beam splitter for autofocus? I assume there is a separate one for autofocus, if one is used in the camera.

Here is a link that discusses a beam splitter for autofocus:

http://photonotes.org/cgi-bin/entry.pl?id=Beamsplitter

Here is the patent:

http://freepatentsonline.com/6339499.html

I currently assume that the XL H1 does not have a separate beam splitter for autofocus. I feel the XL H1 analyzes the image from the sensor to set focus.


I fully understand that most, if not all, still cameras use a beam splitter for autofocus and thus a circular polarizer is necessary.

The filter expert that I spoke with has offered to send me one of both types.
I will report the results of my testing.

Here is another link, in depth discussions of both types:

http://dpfwiw.com/polarizer.htm

[Tony Davies-Patrick]

The main problem is not so much the autofocus but the actual correct metering when using either filter.

If I cannot see any difference when looking at a high quality still image under a high-powered Lupe on a light table, or a large 100GB Tif file on a large quality screen or resulting large print, then I very much doubt that anyone could ever spot any visual difference in the much lower-grade moving image originating from an XL-H1 shot with both types of filter.

[Dan Keaton]

Dear Tony,

That is certainly good information.