nekon Loc: Carterton, New Zealand

There is some confusion on whether to use circular polarizers, or linear ones-they are both circular in shape but they polarize the light passing through them in different ways, You may have read that linear polarizers interfere with auto-focus systems, but as the following explains, the effect is negligable.

The problem is that the percentage of light that is reflected to the focus screen can vary slightly depending on its polarization. Since most cameras meter off of the focus screen image, that can have a small effect on the metering.

Beam-splitters reflect a different percentage of the incoming light depending on the polarization of that light. With a linear polarizer, the light reaching the beam-splitter (viewing mirror) is still polarized, and the direction of the polarization depends on how you have the filter adjusted.

So you see the problem: adjusting the linear polarizing filter will change the percentage of light reflected to the view screen, which in turn will affect the in-camera metering.

But! The difference in the percentage that gets reflected is fairly low for beam-splitters built using an aluminium reflective coating, which is pretty much every SLR or DSLR beam-splitter ever made. It's probably less than 1/3 stop in most cases. Most people will never notice this difference.

TucsonCoyote Loc: Tucson AZ

Now I see what this is all about...the usual....you know, bottom line for polarizer lens makers!

Thanks for the info nekon! :)

busted_shutter

Waiting for the impending fallout!

LoneRangeFinder Loc: Left field

I believe there is also some interruption of AF?

nekon Loc: Carterton, New Zealand

as stated in original, "You may have read that linear polarizers interfere with auto-focus (AF)systems, but as the following explains, the effect is negligable.:

BHC Loc: Strawberry Valley, JF, USA

Thank you for this information. Could you please cite the reference for your post; I would like to add it to a databank I maintain referencing such data.

Nikonian72 Loc: Chico CA

More than you ever wanted to know about Circular Polarizing filters:
http://en.wikipedia.org/wiki/Polarizer#Circular_polarizers

"There are two types of polarizing filters readily available, linear and "circular", which have exactly the same effect photographically. But the metering and auto-focus sensors in certain cameras, including virtually all auto-focus SLRs, will not work properly with linear polarizers because the beam splitters used to split off the light for focusing and metering are polarization-dependent. Linearly-polarized light may also defeat the action of the Anti-aliasing filter (Low-pass filter) on the imaging sensor.

'Circular' polarizing photographic filters consist of a linear polarizer on the front, with a quarter-wave plate on the back. The quarter-wave plate converts the selected polarization to circularly polarized light inside the camera. This works with all types of cameras, because mirrors and beam-splitters split circularly polarized light the same way they split unpolarized light". per Norman Goldberg (1992). Camera Technology: The Dark Side of the Lens. Academic Press. pp. 141–147. ISBN 978-0-12-287570-0.

LoneRangeFinder Loc: Left field

Source?

nekon Loc: Carterton, New Zealand

Experience-I have used both circular and linear polarizers on my D200 with no auto focus problems, and I have contacted a friend who is a qualified camera mechanic, used to work foe H.Perry here in New Zealand

BHC Loc: Strawberry Valley, JF, USA

Thank you.

photocat Loc: Atlanta, Ga

I know of several folks who have done serious testing with both , with the same results. No difference.

One being Jon Greenbro who is Art Wolfe"s assistant and educator on Creative Life

LoneRangeFinder Loc: Left field

OK.

speters Loc: Grangeville/Idaho

That might be true, but it affects different AF systems in different ways, and in some cases throw it off completely. So it is good advice to stay away from linear pol-filters for that reason.

wingincamera Loc: Spanaway, Washington

Just a thought. If you already have a good linear polarizer and use it with a internal focusing lens, couldn't you frame & focus the shot without the polarizer on the lens, then screw on the polarizer and take the photo?

LoneRangeFinder Loc: Left field

You are way too logical....