Linear Polarizer on a DSLR. I think it works?

[jgwong]

I got a set of Cokin filters on last year's RFF Christmas Giveaway (thanks, daveleo!). One of them was a Linear Polarizer. I have a Canon Rebel T1i DSLR and, researching, I was told the Linear Polarizer wouldn't work on it because it would mess up with autofocus and metering, and that I should get a Circular Polarizer instead.

I eventually tried the Linear Polarizer and... I guess it works? Since I don't have any experience with polarizers before, I'm not sure if it's working as it should.

When I rotate the filter I get reflections removed, as well as changes on brightness. Also, the sky gets darker and some colors gain saturation. Autofocus works, never got a misfocus (which I consistently happens with the Red filter; funny that). No metering issues either, I use Aperture Priority and I get good exposures, haven't noticed anything wrong.

So, is everything ok? Or exposure shouldn't change when rotating the filter? Or something else I'm not seeing?

 

[rscheffler]

Sounds like it's working correctly. The meter reading should change somewhat as the polarizing effect strengthens and weakens during rotation. It's been ages since I've used a polarizer and the common wisdom was as you described it, that a circular polarizer was needed for AF and certain in-camera metering systems to work correctly.

I assume you're using the viewfinder for composition and AF? That's when the problem should happen. It's possible that using live view to focus and meter totally bypasses the problem, if it existed (assuming that camera has live view).

 

[jgwong]

I'm using the viewfinder, yes. I have no problems whatsoever. I haven't tried it with Live View (yet).

Maybe the Circular Polarizer requirement is a myth?

 

[Dwig]

...
I assume you're using the viewfinder for composition and AF? That's when the problem should happen. It's possible that using live view to focus and meter totally bypasses the problem, if it existed (assuming that camera has live view).

+1

Live view and its associated contrast AF have no difficulty with linear polarizers, whether it is in a DSLR where it is an option or in a "mirrorless" cameras (e.g. m4/3, ...). The semi-silvered mirrors used in most DSLRs to pipe light through the main mirror, off a secondary mirror and onto the sensor used for the phase detection AF can be blinded by a linear polarizer when it is set to certain angles. This blinding can affect the light meter as well, leading to incorrectly exposed pictures. Circular polarizers eliminate the issues.

 

[jgwong]

The semi-silvered mirrors used in most DSLRs to pipe light through the main mirror, off a secondary mirror and onto the sensor used for the phase detection AF can be blinded by a linear polarizer when it is set to certain angles. This blinding can affect the light meter as well, leading to incorrectly exposed pictures. Circular polarizers eliminate the issues.

This haven't happened to me yet.

So far, I'm quite happy it works. I really wanted to have a working Polarizer!