Polarizers: Circ vs Linear

[Cadenza]

Need advice:

I lost my Circ Polarizer a while ago, and I'm
gonna get a new one. My question is, does
a linear polarizer behave different from a
circular polarizer as far as the image effect
is concerned? Of course, I'm aware that
linear affects a camera's AF, etc.

Also, what's the best cost-benefit polarizer
filter for the 17-40 f4L?

Also, is it too cumbersome to use step-down
rings for polarizing filters? Any caveats?

Thanks, Cadenza

[Persian-Rice]

They don't behave differently, but as you know it will screw with the camera AF. Pretty much, linear wont work on any dSLR.

I use Hoya circ-polarizers, they are pretty cheap and are good quality. I would say it is ok to use a stepping ring, but that is if you have another lens which you want to share it with. I would buy it at 77 mm filter and get a step-up for your other lens.

[Hellashot]

A linear polarizer will work on a dSLR if you only want to use manual focus. Autofocus will not work with a linear polarizer.

[Nightcrawler]

I'm confused, I used a Linear Polarizer on my 20D with my 50/1.8 this weekend. It seemed as though the AF and AE were working just fine. Is it the case that using a Linear will only affect the AF and AE some of the time? Has anyone else tried using a Linear with their DSLR?

[Chazs]

Has anyone else tried using a Linear with their DSLR?

I've tried linear on both my DRebel and my Canon S40. No problem. I'm wondering if it starts to cr*p out under low light conditions. I'll give it a try on my 20D today.

[KennyG]

I've tried linear on both my DRebel and my Canon S40. No problem. I'm wondering if it starts to cr*p out under low light conditions. I'll give it a try on my 20D today.


It has nothing to do with the amount of light, it is the angle that matters. Linear polarizers should not be used with DSLRs if you wish to be certain of AF. The references are their from Canon, Nikon, Fuji, etc.

[Jon]

You shouldn't use linear polarizers because both the AF and the AE sensors rely on partially-reflective mirrors passing some of the light through; the light passing through these mirrors is polarized in the process; if you've used a linear polarizer, you'll be passing already-polarized light through to get cross-polarized light, and an excessive reduction in light values. It'll be more of a problem with AE than AF, but you need to be wary in either case. Circular polarizers have a "de-polarizing" layer behind the polarizer so they're resistant to this problem.