# Pros and cons of circular polarizer filter vs a linear one [duplicate]

There are some similar questions like What is the difference between a linear and a circular polarizer? but I am thinking of a comprehensive list of the pros and cons of the two types of filters.

For example.

Linear

Pros:

• Can be used as a variable ND density filter when combining two of them.

I am asking this becouse I have not used a circular one, and I am not sure how effective is to reduce reflection on glass for example, so there can be some categories on the technical aspect, like autofocus issues and the photographic results.

So the question is: What are the Pros and cons of circular polarizer filter vs a linear one?

What is called a "circular polarizer" in photography is just a linear polarizer combined with a quarter wave plate which converts the linear polarized light that comes out of the first part of the filter to circular polarized light. The conversion to circular polarized light makes the light behave the same as unpolarized in the camera thereby preventing the problems mentioned in WayneF's answer.

To construct an ND filter you can use a linear polarizer and behind that a circular polarizer. The quarter wave plate at the end then converts the linear polarized light that passes through both the filters to circular polarized light, so you are still free of problems.

A circular polarizer in the meaning of a filter that lets through only the left handed or right handed helicity component of light is just what you get if you flip an ordinary circular polarizer. The light then passes through the quarter wave plate first, which means that left handed helicity gets transformed to linear polarized light in one direction while the right handed component gets polarized in the orthogonal direction, the subsequent linear polarizer will then act on that linearly polarized light, it will let through only one component. What is then missing is another quarter wave plate to convert the linear polarized light back to left or right handed polarized light.

You need to understand the situation better, about the purpose of the circular polarizer, about why linear polarizing filters are Not used on sophisticated cameras today.

A linear polarizer will work just fine as far as the photo goes. The photo does not care. We used linear filters in the old days (before electronic sensors).

But a linear polarizer runs strong risk of interfering with the DSLR cameras AF and metering functions. They simply are not designed for polarized light.

See this warning from Lee filters: http://www.leefilters.com/index.php/camera/polariser

See this warning from Wikipedia: http://en.wikipedia.org/wiki/Polarizing_filter_%28photography%29

See this warning from Tiffen filters: http://www.tiffen.com/polarizer_pics.htm

See this warning from Hoya filters: http://www.hoyafilter.com/hoya/products/generalfilters/plplcir/

Could go on forever, but also read what your camera manual tells you.

For one example, page 236 of Nikon D5300 Reference Manual:

"The D5300 can not be used with linear polarizing filters. Use C-PL or C-PL II circular polarizing filters instead".

This will not convince everyone of course. :)

The one redeeming factor, if you will NOT use the cameras metering or AF functions, then the linear polarizing filter will still work fine.

No question, the polarizer is the most useful filter in arsenal of the digital photographer. The polarizing screen works because light from the sun as well as many light sources is un-polarized meaning the light waves vibrate in any and all plains. As the light passes through the atmosphere the direction vibration is altered. This vibration orientation is also changed when light sticks certain objects. The polarizing filter works by selectively allowing light waves that vibrate in only one direction to pass. The photographer is required to fine tune the effect of the filter by rotating it for best effect. The net effect is the polarizing filter darkens clear skies causing white clouds to stand out. Additionally, the polarizer can subdue reflections from glass, water, and most non-conductive surfaces. The polarizer also acts as a UV haze cutting filter. The bad news is, it cuts light transmission by 2 full f/stops.

The best effects are effects are realized when the sun angle relative to the camera is 90°. The polarizer is also a great help when doing copy work, it can help minimize reflections. This time the best effect occurs when the copy is illumined using lights set 33º to the horizontal.

Two types of polarizer screens are available. Both function alike to reduce reflection and increase saturation. Circular polarizers are the preferred type for the digital camera. The Circular is made by sandwiching two filters together. One layer is a standard linear polarizer; the other layer is a retarder. The retarder sits facing the camera. It de-polarizes after the linear layer has done the deed. The circular polarizer is less likely to interfere with auto focus and exposure determination mechanism. However some digital camera designs tolerate a linear polarizer.