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Old June 30th, 2008, 04:17 PM   #1
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Interesting PL Filter discovery

Hey guys.

Recently I got myself a new PL filter from Hoya, replacing my old cheapo filter from Mercury Optics.

The interesting part occured when I paired the two filters together.

Depending on which filter is attached to the lens first, the two filters can function as a varriable ND filter, or a white balance shifter. I dont know if this discovery has any practical use, but never the less I find it quite interesting, and would like to share it with the rest of you.

Video link: http://www.infinitive.dk/pl/
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Old July 4th, 2008, 08:30 PM   #2
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Further testings show that the POL Filter pairing seems to be very usefull as a Iris ring/ND filter alternative..

You will have the option to adjust the exposure in a stepless maner while shooting, very much like a Iris ring, but still maintain the same DOF. That would be very usefull in situations like, on a sunny day, where clouds change the exposure every time they cover the sun, and many other situations.. Basically every situation where you would use the Iris ring, you can use the POL filter feature, with greater control, and still no change to DOF.

I would suggest any lens manufacturer to investigate in this, and figure out why this feature happens. Strip off the unnecessary POL filter characteristics, leaving the glass only to keep what makes this "magic" happend, and develop it effectively replacing adon ND filters forever.
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Old July 5th, 2008, 10:10 AM   #3
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This is actually a well known effect (it should be if I know about it ;-). If you ever had polarizing sunglasses you may have noticed the effect when looking at LCD screens or other polarized sources.

Another film/video use is this: http://www.rosco.com/uk/video/roscoview.asp. Where you cover windows and can then adjust the intensity of the outside.

Pola's are fun!

George/

Last edited by George Kroonder; July 5th, 2008 at 03:40 PM.
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Old July 5th, 2008, 02:30 PM   #4
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If you think of light waves as bunches of worms traveling through space while wiggling in all directions. then a polarizing filter is sort of like a picket fence - when the worms hit it, only the worms wiggling in more or less the same direction as the openings in the fence can get through. If you put another fence at right angles to the first one, none of the worms can get through. If the second fence is parallel to the first one, then almost all of the worms can get through.

The effect of impurities or stress in glass or plastic wll modify the polarization of the light, and can be seen clearly with crossed filters.

http://home.comcast.net/~cassarole/CrossPolarizer.html
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Old July 5th, 2008, 04:51 PM   #5
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I'm a still photographer, if you PL try this one, I used this one
http://www.singh-ray.com/goldnblue.html
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Old July 5th, 2008, 08:56 PM   #6
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oh well thats cool... So I wonder why Tiffen, B+W, Hoya and the rest of them, havn't replaced their "static" 2 - 4 - 8 ND filters with a varriable one yet.. Which when you turn it makes a "tick" and everytime it ticks, you add density in controllable repeatable increments, with the option to turn the tick off, and ad density totally seamless while shooting

Or why most build in ND filters embeded inside the lens only have like 2 varriables. Would be much cooler if you could have total control, from 2 to infinity.
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Old July 5th, 2008, 11:19 PM   #7
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Maybe price?
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Old July 10th, 2008, 09:45 AM   #8
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Quote:
Originally Posted by Nik Skjoth View Post
oh well thats cool... So I wonder why Tiffen, B+W, Hoya and the rest of them, havn't replaced their "static" 2 - 4 - 8 ND filters with a varriable one yet.. Which when you turn it makes a "tick" and everytime it ticks, you add density in controllable repeatable increments, with the option to turn the tick off, and ad density totally seamless while shooting

Or why most build in ND filters embeded inside the lens only have like 2 varriables. Would be much cooler if you could have total control, from 2 to infinity.
This is not actually a variable ND filter but rather a simple matter of cross polarization. The decrease in light transmission is caused by polarization in both directions. This is called extinction ratio. The extinction ratio is rated by the ability of the filter to block light when cross polarized.

The problem with cross polarization is that the image tends to shift to the blue end of the spectrum (500-600 nanometers). This would be no big deal except for the fact that it causes uneven color cast and is almost impossible to white balance. If you have access to gamma controls (Varicam, etc) you could play with the channels and get it better. The reality there is that if you are doing that, you most likely won't be using a trick filter like this which would mostly serve as a cost saving function over buying 4 or 5 different ND filters.

Ryan Avery
Schneider Optics
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