How can you tell the difference between a Linear & Circular Polariser?

Wail

Wail

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Wail
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I've never understood the difference other than for digital we ought to be using Circular (somehow Linear seems to push the metering all over the place); but my question is ... if I have a Polariser in my hand, how would I know if it's a Circular or a Linear?

Thanks for any feedback.
 
Wail said:
I've never understood the difference other than for digital we ought to be using Circular (somehow Linear seems to push the metering all over the place); but my question is ... if I have a Polariser in my hand, how would I know if it's a Circular or a Linear?

Thanks for any feedback.
Click to expand...

Other by reading what it says on the rim, I don't know!
 
If you have two place one in front of the other and rotate them if at some point you can no see through them both it will be linear if you can see all the time then circular mind you not sure if you have one of each lol
thought try with some sunglasses they are linear.
 
jerry,

True :p .. but I mean other than that ... let's say for argument's sake the text on the filter is wrong :shrug:
 
Chaz,

I don't have a LP .. so I can't really test for that :shrug:
 
Chaz Photos said:
as I said try sunglasses if you can see when you rotate it all round then you will have a CPF if you find a point you can see then its a linear
Click to expand...

(y) .. thank you for that.

Now, as funny as this may sound, I don't have a pair of sunglasses (even though I live in a country that's sunny 24/7 :p)

Will run off to an optician to test this out :)
 
You can't tell by looking.

Linear Pols apparently affect AF but I have one and it works fine and the same as a C-Pol!
 
place it up to a mirror... if you can see through the polariser and see through the 'back' of the polariser back to you from the reflection in mirror, then you've got a linear version.

if it's completely black then you have a circular.

Ads :D
 
adsayer said:
place it up to a mirror... if you can see through the polariser and see through the 'back' of the polariser back to you from the reflection in mirror, then you've got a linear version.

if it's completely black then you have a circular.

Ads :D
Click to expand...


Never knew that. Brilliant idea, just tried and it works.
C
 
Try it out. If everything works then it doesn't matter. If the camera doesn't focus or meter correctly then it's probably linear.

I like the mirror test though!


Steve.
 
Anytime guys... it's a quick and handy way to tell the difference :D

puddleduck said:
You can't tell by looking.

Linear Pols apparently affect AF but I have one and it works fine and the same as a C-Pol!
Click to expand...

I found this also... strange!
 
Not sure if this works on a linear (can someone check?)

Place the polariser back towards an LCD screen (IE laptop) and rotate it. At some point, you wont be able to see the screen display at all....
 
adsayer said:
place it up to a mirror... if you can see through the polariser and see through the 'back' of the polariser back to you from the reflection in mirror, then you've got a linear version.

if it's completely black then you have a circular.

Ads :D
Click to expand...

Not quite true.

It depends which face is to the mirror. You will see a change in the 'ND' effect.

One way around, the circular polarizer will cut out about 75% of the light, the other way around, it will cut out 25% of the light with the test above.

If you had a linear polarizer, you would see no difference in the 'ND' effect, whichever face you had to the mirror.
 
OutLore said:
Not sure if this works on a linear (can someone check?)

Place the polariser back towards an LCD screen (IE laptop) and rotate it. At some point, you wont be able to see the screen display at all....
Click to expand...

Both filters might produce the same effect (yes, a linear will at one angle, no matter which face is towards a normal LCD panel (one without a glare filter or de-polariser incorporated) be completely black)
 
I suppose the real question is - as at least 3 of us have or are using Lin-Pols with AF just fine.. do we actually need C-Pols.. I'm not sure why AF works, but it does.
 
adsayer said:
place it up to a mirror... if you can see through the polariser and see through the 'back' of the polariser back to you from the reflection in mirror, then you've got a linear version.

if it's completely black then you have a circular.

Ads :D
Click to expand...

That's an interesting method to check it out. Would have never crossed my mind. I don't have LP to check that, but I will test with the CPs that I have.

Thanks.


puddleduck said:
You can't tell by looking.

Linear Pols apparently affect AF but I have one and it works fine and the same as a C-Pol!
Click to expand...

Actually, it's because of this that I am thinking of getting LP instead of CPs. With the huge price difference, and a number of threads that I've read here, and elsewhere, where LPs are said to be just as good. I thought I'd give this a go and see what happens.


Steve Smith said:
Try it out. If everything works then it doesn't matter. If the camera doesn't focus or meter correctly then it's probably linear.

I like the mirror test though!


Steve.
Click to expand...

Very logical, and I can't dispute that approach. Will surely give it a go with one LP to see how things work out.


coldpenguin said:
Not quite true.

It depends which face is to the mirror. You will see a change in the 'ND' effect.

One way around, the circular polarizer will cut out about 75% of the light, the other way around, it will cut out 25% of the light with the test above.

If you had a linear polarizer, you would see no difference in the 'ND' effect, whichever face you had to the mirror.
Click to expand...

OK, just when I thought there was an easy method for me to test this .... now it's back to being all complicated :p

I guess I'd just better try it out and see what results I get.


puddleduck said:
I suppose the real question is - as at least 3 of us have or are using Lin-Pols with AF just fine.. do we actually need C-Pols.. I'm not sure why AF works, but it does.
Click to expand...

Would you mind telling me which brand of LP you're using. I'd hate to find that this works for one brand and not another (knowing my luck, I'll be stuck with a LP that doesn't exactly work).
 
Thanks for all the answers so far.
 
Wail said:
Would you mind telling me which brand of LP you're using. I'd hate to find that this works for one brand and not another (knowing my luck, I'll be stuck with a LP that doesn't exactly work).
Click to expand...

B&W TOP Pol.
 
Aha, great .. time to order one then (y)

Thanks
 
I use the following Linear polarizers, no problems.
For some cheaper types of Auto-Focus, there were problems with Auto-Focus. However, in modern day, non-compromised auto-focus systems, you should not be getting problems with linear polarisers. The problem you might have, is a lack of light comming in, which would be the same with a CPL.

Quantaray LPL
Unknown Brand LPL - Made in Korea
Hoya Purple LPL
Jessops LPL

The mirror test will work, just make sure you turn it round so that you try it with both faces.
A circular polariser, is effectively two filters. It has a linear polariser on one face, and then a 'diffuser' on the second face. The second filter un-polarises the light.
For 'cheap' auto-focus systems, they split the beam and then re-combine it. IF the beam is only 1 angle of polarisation, there can be diffraction effects, which might effect the result. With a Nikon camera (don't remember seeing what it is specifically), I do not think you will have an issue.
 
is there a front and back to a cokin p circular polariser ?

i always have the side with the writing on away from the camera , is this right ?
 
I honestly haven't a clue on Cokin; sold all my collection a while ago, after not having used them for a few good years. Sorry, may be someone else can help in this.
 
Easy way to tell circular and linear polarisers apart, if you have an LCD computer screen.

Circular - looking through the filter from the lens side, as you rotate it the screen will go black. Turn the filter over so that you are looking though it back-to-front, and as you rotate it the screen will not go black.

Linear - as you rotate the filter, the screen will go black whichever way you look through it.

As I understand the problem with AF systems and linear polarisers, it is similar to the effect above when looking at an LCD screen, which is polarised. The half mirror in the camera also partially polarises the light as it is fed to the AF sensors. When the two polarised planes coincide, the light to the AF sensors is substantially reduced, leading to potential errors in certain situations.

But if it works, it works, so no major problem with AF. Perhaps more of a problem is when metering systems are also fed by polarised light which could lead to errors that would not be immediately obvious until after the picture was taken. However, I don't think many cameras have this kind of metering these days.

The other problem with linear polarisers is getting a good multicoated one at sensible money. Hoya don't make a top quality linear at all, and the B+W/Heliopan etc linears cost more than a Hoya Pro1 circular polariser.
 
Thanks, now that was easy to test with a CP .. which I did :)

As I said in my earlier post, I want to get a LP to play with and see what results come out of that.
 
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