Polarisers - Linear, Circular

[ameerat42]

Hi All.
It is with some reservation that I open this topic, but I would like some clarification on terminology, and where better than to poll this forum?

I have looked up lots of references to do with, in particular, Circular Polarisers - I fancy I know a bit about Linear Ps, which I have used a lot - only to find that many of the explanations seem to falter at the critical point of explanation. I'll summarise my gleanings to help. They are few but...

1) Circular Ps are required instead of Linear Ps in modern cameras so as to allow their AF and metering to work properly. (Took a few articles to find out why, but OK.)

2) A Circular P is made up of a Linear P and an integrated "half-wave" plate. OK, this helps make it work as a "Circular" P.

3) A circular P is actually a minsnomer because it DOES NOT polarise light "circularly" - a fast becoming disliked word, which I'll shorten to ccly.

At point 3) I start to lose the idea, ESPECIALLY, when the directions "left-" and "right-" "ccly polarised" add to the blur.

So, can someone set me straight? Can someone even refer me to an (even arcane would be acceptable) illuminating article on the topic? Please don't say Wikipedia as I've looked at their several references. I've gone about two pages into a Google search headed "circular polariser".

Thanks in advance. Am.

[Wobbles]

Hi,
have a look here http://www.geocities.com/cokinfiltersystem/polarizer.htm

and for more detail here http://www.mat.uc.pt/~rps/photos/filters_uv_pol/#polq2

to get a "reasonably" simple explanation of how they work, the difference and why you need a CPL for most modern cameras.

Cheers
John

[arthurking83]

I have and use both!

they seem to work exactly the same.

Granted I do get irregular focusing issues with the LPol, but it's so irregular and generally in low to very low light.

As for the resultant images.. buggered if I can see any difference in the absolute quality in the images.

There are two distinct differences between my CPol and LPol filters tho, and that is simply colour tone.
The L gives more of a green cast to the images and the CPol gives more of a red cast.
I generally leave my camera to AutoWB and that's the major difference.
In adjusting the WB in my raw converter of choice, I can balance the images to look pretty much the same by using the tint slider in equal, but opposite amounts.

As for 'white papers' on what, how, why and if they make a difference.. I have no idea! My only concern is to understand if they make any difference in real life conditions.

And to be honest the differences I see between my two filters, I personally prefer the greener colour cast of the LPol, as grass looks yuk with a red cast.

I've used my LPol from all focal lengths starting at 10mm, ending @ 20mm, restarting at 70mm and finishing at the 200mm end of the focal length scale. As far as I can currently make out, the LPol focusing issue is not enough of an issue to make it an issue to worth worrying about.

If you have Linear Pols use them, unless you are having focusing and metering problems.

If you do find any more info the differences between L's and C's be sure to post the link. :th3:

[dbax]

very interesting post, thanks, I've bookmarked this one

[ameerat42]

Thanks John and Arthur. I didn't see the 1st ref in my travels yesterday and anyway, I have now bookmarked both. I think it's coming along very well, the only sticking point seems to be the term "circular", but as the effects and operation of the two filters are pretty well explained, I'll let that other point go.
Ta. Am.

[Wobbles]

Thanks John and Arthur. I didn't see the 1st ref in my travels yesterday and anyway, I have now bookmarked both. I think it's coming along very well, the only sticking point seems to be the term "circular", but as the effects and operation of the two filters are pretty well explained, I'll let that other point go.
Ta. Am.

Hi Am,
this one should hopefully clarify the "circular" bit... http://www.bobatkins.com/photography/technical/polarizers.html ...get your skipping rope out and start practising :rolleyes:

Cheers
John

[CapnBloodbeard]

I use a linear on my 30d with no problems.

[ameerat42]

Thanks guys. John, yes, I saw that one and found it one of the more helpful ones. Am.