Ciruclar Polarizer Question

[natelam]

I'm a newbie with the polarizers. I originally bought one from a local shop (B+W F-pro) then returned it because I realized it was ridiculously over priced.

When playing with this polarizer, turning the front changed the darkness of the element from clear, to dark (almost like a graduated filter).

My new filter (B+W Slim) circular polarizer, I don't have this same effect, turning the front element doesn't have any obvious effect on the filter (except probably just to change the angle of polarization).

My question is, why did the first filter do this, and why doesn't the second? I've never had one before so I'm not sure which is correct, and why one would behave this way and not the other. The only difference between the two are slim and non-slim versions.

Help!

 

[Chris101]

Were you wearing sunglasses when you examined the first filter? 8)

When you cross polarization planes at right angles to one another, the filter goes dark. If you weren't wearing polarized glasses, were you looking at it with reflected illumination? Reflected light gets polarized too.

 

[natelam]

I was examining it indoors, with a desklamp on, but I'm doing the same exact thing, in the same exact location with the new filter...can't seem to simulate the effect.

Perhaps it was just the right moment with just the right lighting? Nothing wrong with my new filter right? What's the best way to test it? View an LCD clock with it and see if the numbers dissapear at the right angle?

 

[natelam]

Just realized the possibility that the first filter they sold me could have been a linear polarizer even though the box said circular (the seal was broken). Odd.

 

[Chris101]

Hi again Nate, I got out a circular polarizer and linear polarizer, and played with them under a few different lighting situations. I couldn't get either one to react the way you described the first filter as doing. I'm thinking that you were seeing light that must've passed through the filter once, then reflected back through it. This is kind of Warren commission thinking I know.

I did however notice something very interesting. My linear filter works the same frontwards or backwards. That it it doesn't matter if I look through the front or the back, it polarizes the light just fine.

The circular polarizer, on the other hand, only worked when looking from the lens side to the subject side. When reversed it was just a neutral density filter, with no polarizing quality. Well, some, but maybe only 5% of what it was the other way around.

This is strange, but may be a way to test if a given filter is circular or linear. Oh, and the LCD test didn't work for me with either filter - the LCD did however, get colored bands on it that moved when I rotated the filter.

 

[AndyE]

My question is, why did the first filter do this, and why doesn't the second? I've never had one before so I'm not sure which is correct, and why one would behave this way and not the other. The only difference between the two are slim and non-slim versions.

Help!

Nate,
are both filters of the same type?
green (=uncoated)
blue (=coated)
HMC (=Multi coated)

some websites with info's on polarizing filters:
http://www.geocities.com/cokinfiltersystem/polarizer.htm
http://www.photofilter.com/camera_filters.htm
http://dpfwiw.com/filters.htm#polarizers

you also might try the filter section at photo.net:
http://www.photo.net/bboard/q-and-a-one-category?topic_id=1544&category=Filters

kind regards,
Andy

 

[natelam]

both the same exact kind, only difference was slim vs non-slim. I'm stumped, thanks for all the resources, went through them all!

 

[GMolotsky]

Nate,

Chris pretty much hit the nail on the head as far as what happens with polarized light. I've read through what you said happened and am stumped as well. Some silly questions: Was there any type of filter on the camera already? Is it possible the 1st filter was two slim linear polaizers attached together with you only moving one?

Gregg

 

[natelam]

The test was actually just turning the filter looking at my hand through it, not on the camera. No possibility of having 2 filters together, was out of the box from the store, had threads on it, definately not 2 slim polarizers (besides if it was, I'd have kept both! Deal of the century j/k=)

 

[GMolotsky]

Nate,

Well then the light that was going through the polazier had to be polarized from some other source and you are probably right that you had a linear, not a circular polarizer the 1st time. What that source was, who knows. Just enjoy the new filter.

Gregg