Circular Polarization

[davidhudson]

Hi.

Can anyone explain in, layman terms, why digital cameras, still and

video, need to have circular polarizing filters rather than linear?

Thanks

David Hudson

[patrick_kelly6]

http://www.luminous-landscape.com/tutorials/polarizers.shtml

 

You might take a look at the link above. It explains, very briefly, why you need circular.

[david_haynes]

I've continued to use my linear polarizers with all my digital cameras and haven't had

any problems so far.

 

My understanding of the need for circular polarizers is that the linear ones interfere

with some TTL metering systems and some AF systems.

 

I carefully tested my old-style linear polarizers with my Canon DSLRs, Canon G5 and

Leica D2 and have found that they work just fine.

 

I have been told that one instance when linear polarizers do not work is with camera

meters (like the Nikon f3) which use a split/hinged mirror that opens at the moment

of exposure to take the meter reading.

 

I guess my Canon DSLRs and other digitals do not do this. Regardless, I can't justify

spending money on circulars to replace the linears I already have if they are not

causing problems.

 

If like me you have linear polarizers already, I'd suggest you test them to determine if

they work. If so, just use them; if they don't work, spring for the circular.

[godfrey]

The article at Luminous Landscape says:

<br><br>

<hr>

<i><b>Circular Vs. Linear Polarizers</b>

<br><br>

There are two types of polarizing filters available - linear or circular. Linear polarizers are

more effective and less expensive than circular ones. But circular polarizers are needed

with just about any camera that has a through-the-lens metering system, or autofocus.

<br><br>

The reason for this is that both of these systems use semi-silvered mirrors to siphon off

some of the light coming though the lens. If that light is linearly polarized it renders either

the metering or the autofocus ineffective. This means that you're going to have to buy

circular polarizers unless you're shooting with a pre-1970's camera, or a view camera.

</i>

<hr>

<br><br>

This is not accurate. You should use a circular polarizer if the camera uses beam splitters

and other types of light pipes which include an inherent polarization mechanism for

consistency in focus and exposure evaluation. While most (but not all) modern SLR

cameras fall into this category, very few digital cameras do.

<br><br>

I use a circular polarizer with my Canon EOS system bodies because they do use beam

splitters in the mirror to send light to AF sensors and metering unit. However, neither my

Sony F707/717 or Panasonic FZ10

require a circular polarizer as there is nothing that can polarize the light in the lens path

to get confused by the additional polarization.

<br><br>

Godfrey

[bobatkins]

Any camera with a semi-silvered reflex mirror (which is just about every current AF SLR and DSLR) requires a circular polarizer for accurate metering under all conditions. In theory some AF systems could be affected, but this is more of an urban myth than an actual problem.

 

There's nothing inherent in DIGITAL that requires a circular polarizer. If the camera doesn't use a partially reflecting reflex mirror, a linear polarizer will be fine.