Poralizing Filter

[ESEA]

First of all, I am new here so Hi to all.
I just got out my old filters off my old film Canon T70 camera (unfortunately the lenses are shot, too many years living on yachts and the coatings have started to delaminate)
I would like to use my old filters on my new digital. I have no idea if Polarizing filter is Linear or Circular? Is there a way of telling? It is a Vivitar 52mm PORALIZING
Thanks for the help

[Paul2660]

A CL-PL will allow you to rotate the filtler 360 degrees and as you rotate it, you will either be increasing or decreasing the amount of polarization.  I also believe that a linear Polarizer has no adjustment ring as it's effect is constant.  

This is a easy thing to see on a subject that easily shows the effects of polarization like glare on water or sky.   As you turn the adjustment ring, you can see the effect of the polarization on the subjet gradually increase, then after you get to the max amount of Polarization it will start to decrease.  

Paul C.

[ESEA]

A CL-PL will allow you to rotate the filtler 360 degrees and as you rotate it, you will either be increasing or decreasing the amount of polarization.  I also believe that a linear Polarizer has no adjustment ring as it's effect is constant. 

This is a easy thing to see on a subject that easily shows the effects of polarization like glare on water or sky.   As you turn the adjustment ring, you can see the effect of the polarization on the subjet gradually increase, then after you get to the max amount of Polarization it will start to decrease. 

Paul C.
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Thanks, it's that simple! I feel dumb. The filter has a adjustment ring so I have a Circular Polarizer. I had read somewhere that for through the lenses auto focusing cameras you had to have a Circular Polarizer

[dobson]

Please correct me if I'm wrong. I have both circular and linear polarizers and they both have rotating mounts allowing you to adjust the amount of polarization. The purpose of a circular polarizer is that AF sensors do not function properly in polarized light; so the polarized light is "un-polarized" (made circualr) by a second layer in the filter. this results in a filter that only functions properly when light passes through it in the right direction, (if you mounted it backwards it would not function properly in crossed polarized situations). To find out what you have, you need two polarizers, (polarized sunglasses work). If you stack the two filters, you should be able to rotate them in relation to one-another and have the resultant light black completely out. With circulars this only works when the filter is being held the correct direction; with linears it should work regardless of what side is facing you.

if any of this isn't clear just ask

[dobson]

One question; are you shooting a DSLR or a fixed lens digital with an EVF. You only need a circular if you are shooting an SLR style camera with the semi-silvered mirror.

[boku]

Please correct me if I'm wrong. I have both circular and linear polarizers and they both have rotating mounts allowing you to adjust the amount of polarization. The purpose of a circular polarizer is that AF sensors do not function properly in polarized light; so the polarized light is "un-polarized" (made circualr) by a second layer in the filter. this results in a filter that only functions properly when light passes through it in the right direction, (if you mounted it backwards it would not function properly in crossed polarized situations). To find out what you have, you need two polarizers, (polarized sunglasses work). If you stack the two filters, you should be able to rotate them in relation to one-another and have the resultant light black completely out. With circulars this only works when the filter is being held the correct direction; with linears it should work regardless of what side is facing you.

if any of this isn't clear just ask
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You are correct. Paul C is in error and the advice should not be used.

[ESEA]

dobson: Just got my P-sunnies out and placed it in front of the P-filter, Rotate and I get black out, then I turn the P-filter over (now the thread is away from me) rotate and again I get blackout. Therefore what you are saying is I have a Linear P-Filter   This is bad as I believe (correct me if I am wrong) I have a DSLR it is a PANASONIC LUMIX DMC -FZ7  
This all said and done, it has manual focus as well, so if using the MF I can still use my P-filter?
Paul C not to worry! this is what forums are all about .. sharing info and learning form one another.

Now this is what I speculate that a linear is like a set of Venetian blinds, blades horizontal or strait up and down... circular would be more like the blades wrapped around with the ends touching and each blade increasing in diameter.

[dobson]

A little more research showed TTL metering works with a linear, but not properly. The problem is that if the polarized rays hit the semi-transparent mirror at the wrong angle, the light will not be diverted properly to the sensor resulting in strange, even blacked out, readings. You can still work around this by using MF and bracketing exposures (start out at a one stop increase from the non-filtered exposure), if you don't really want to go out and purchase a new filter at the moment. The photographic results should be the same it's just more hassle. (it turns out that because linears do not have an extra wave plate the image quality is generally better)

I used to think exactly as you do about the differences between linear and circular. But it turns out that they polarize light exactly the same way (like blinds). The difference of a circular filter is that after the polarized light is filtered it is passed through 45 degree quarter-wave plate that separates the waveforms. Instead of waves oscillating the same direction, they are sent oscillating in a circular pattern.


This stuff is really interesting. The designers of polarizers sure know what they're doing.