Circular Polariser Filter

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Brian
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I recently bought a "Kenko" brand circular polariser filter, and I'm not sure it's doing it's job correctly.
With other polarisers I've had, you can see the polarising effect by looking at the blue sky and rotating the filter (with the sun at 90 deg)
With this filter the polarising effect when viewed this way, is hardly visible.
What's more, if I view another polariser through the filter, I was expecting, as I rotated the filter, there would be a position where the combined effect of the two polarisers would produce a completely black filter, which allowed no light to pass. This does not occur, and there is only a small effect on the density of the filters.

Have I bought a duff polariser?
 
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Hi,
Circular polarizer is for AF lens,
for manual focus lens you would require Linear polarizer, but then you might know this already
Hope that helps.
 
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5,573
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I recently bought a "Kenko" brand circular polariser filter, and I'm not sure it's doing it's job correctly.
With other polarisers I've had, you can see the polarising effect by looking at the blue sky and rotating the filter (with the sun at 90 deg)
With this filter the polarising effect when viewed this way, is hardly visible.
What's more, if I view another polariser through the filter, I was expecting, as I rotated the filter, there would be a position where the combined effect of the two polarisers would produce a completely black filter, which allowed no light to pass. This does not occur, and there is only a small effect on the density of the filters.

Have I bought a duff polariser?
Sounds dubious. There are fake filters around. Did you try combining the two polarisers in different orientations? With a circular, the effect only works as expected if you view it from the back (as the camera will see it), not the front.
 
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Duncan
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Hi,
Circular polarizer is for AF lens,
for manual focus lens you would require Linear polarizer, but then you might know this already
Hope that helps.
Close but as I understand it, that's not quite right. It's not the lenses that require circular or linear respectively, it's the cameras and their meters. Filters affect camera light meters not autofocus sensors.
 
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Brian G
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Brian
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Easiest, controlled way to see an effect is looking through it on an angle at a TV.
That certainly didn't work.
The only thing I can see is a slight colour shift as I rotate the filter.
(Appplies to both a Hoya and the Kenko filters.)

Edit: Just tried "Retune's" suggestion of looking through the polariser from the "back" or camera direction, and it works! I can black out my TV screen completely, so I presume the polariser is working correctly.
I never knew they were directional like this!
 
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That certainly didn't work.
The only thing I can see is a slight colour shift as I rotate the filter.
(Appplies to both a Hoya and the Kenko filters.)
From the back and front of the filter? (see above). How about when viewing an LCD, like the one on your camera, or the device you are reading this on?
 
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Brian G
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Brian
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From the back and front of the filter? (see above). How about when viewing an LCD, like the one on your camera, or the device you are reading this on?
All looking from the "front" of the filter.
The only times it behaves like I'm expecting is if I view from the "lens" side.
As I said, I never knew these things were directional - thanks for pointing it out.
 

Nod

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Nod (NOT Ethel!!!)
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That's the difference between circular and linear polarisers (well, how it was explained to me some years back!) Linear pols simply polarise the light and send the polarised light straight to the recording medium but circular pols have an extra layer that rerandomises the light after it's been polarised but leaves the effect that the polariser has already added.
 
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Duncan
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That's the difference between circular and linear polarisers (well, how it was explained to me some years back!) Linear pols simply polarise the light and send the polarised light straight to the recording medium but circular pols have an extra layer that rerandomises the light after it's been polarised but leaves the effect that the polariser has already added.
Yep, that's how I understand it, too. A circ pol is a combination of a linear polariser and a quarter wave plate, the latter causing the light let through to be circularly polarised.
 
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All looking from the "front" of the filter.
The only times it behaves like I'm expecting is if I view from the "lens" side.
As I said, I never knew these things were directional - thanks for pointing it out.
Sorry, yes I'd posted that before I saw your edit. This behaviour of the filter surprised me the first time I noticed it!
 
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