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Old December 1st, 2002, 05:04 AM   #1
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do Polarizers make a difference?

Just wondered how many of you are using Polarizers - tried them - and what one do most of you recommend? I tried a circular "Hoyer" one and couldn't see a difference so took it back for a refund. How good are the more expensive - warming polarizers?

I'm looking to darken the blue sky as much as possible without making the foreground too dark. Any tips?

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Old December 1st, 2002, 09:20 AM   #2
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There are two types of polarizer: linear and circular. The circular is what you should use with DV cameras. You want to get on of the adjustable ones so you can dial in the amount of filtration you want.

I never shoot outside without one, they are great for darkening skies, saturating colours and reducing the harsh contrast inherent with video.

Any Japanese made polarizer will do the job you want, avoid Korean made ones as the glass is second rate. I have a couple of different brands, Hoya and Kenko, and they both do the job well. If you can afford to spend a little more get a Tiffen.
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Old December 1st, 2002, 12:57 PM   #3
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There was probably nothing wrong with the polarizer you returned. You have to understand what polarizers do and when they will work.

1. They darken areas of the sky that are 90 degrees from the Sun. The effect falls off the closer one gets to the axis of the Sun (draw a line from the Sun to you . . . that's the axis of interest).

2 They will also 'remove' some reflections from glass and other shiny surfaces (Like water) as long as the light that is causing the reflection is itself, polarized. Doesn't work for light bulbs unless you place a polarizing filter on them too.

The adjustment mentioned by Adrian is that most polarizers can be rotated on their mount. That allows you to dial-in what you want from no effect to maximum effect.

If you have a camera that focuses by rotating the front of the lens (very few permanently attached lens today) then you will have to first focus and then adjust the polarizer.

A polarizer is something to use with some caution as it can make scenes look overly color saturated. As with all filters, use with some amount of caution.
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Old December 1st, 2002, 01:04 PM   #4
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thanks for your replies. I tested the same polarizer, but 49mm, on my still camera to compare and I didn't notice any change on my pd150 when fiddling with the iris and ND filters.
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Old December 1st, 2002, 01:41 PM   #5
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I'm not sure what effect or difference you were expecting to see when 'fiddling with the iris or with ND filters', as that would primarily make a difference only to the exposure.

You would expect to benefit from a polarising filter if your subject included reflections off water, for example. By rotating the filter you might largely eliminate these reflections. Don't anglers use polarising sunglasses so they can see fish more clearly beneath the surface?

And you would certainly see a marked difference to the blue of the sky ... ah, but in Wales, isn't the sky always the colour of Tupperware? :-)

There was a series of architectural programmes on TV in the UK recently in which a polarising filter had pretty obviously been used. The skies were so blue you'd never have thought they were in the UK at all.

Al
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Old December 1st, 2002, 02:29 PM   #6
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Yes, that's the effect I'm after.

Looking at the polarizers at BHPhotoVideo.com, it is quite hard to make a decision on how much to pay. What polarizers do all you have and how much?
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Old December 1st, 2002, 03:29 PM   #7
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Once again in this tread the circular polar is being advised as necessary. This is not true, a linear does a perfect job for video, at least as good as a circular. Another misconception is that "the light causing the reflection should be polarized itself". All light hitting (electrically) non conductive reflective surfaces get linearly polarised, also the light from lightbulbs. The amount of polarisation (thus the degree to which reflections can be suppressed) depends on the angle of incidence and refractive index ratios. Complete polarisation will be at an incident (and reflection) angle of about 50degree for water and glas reflections.
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Old December 1st, 2002, 07:42 PM   #8
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Andre,

Correct me if I'm wrong, but I thought you couldn't use a linear polarizer with 3 chip DV cameras due to the use of a light splitting prism to seperate the RGB beams and send them to their respective CCD.
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Old December 1st, 2002, 07:52 PM   #9
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This is an on going debate that will not be resolved in the near future. However, Canon does make a three filter set for the XL1/S and the Circular Polarizer is what Canon sells in the kit. I hope this helps.

Jeff
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Old December 1st, 2002, 08:43 PM   #10
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For the umteenth time, I use a linear on my VX2K and TRV20 and have never had a problem. Before you discount Andres advive , you may want to check his credentials.
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Old December 1st, 2002, 08:53 PM   #11
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I have the utmost respect for Andre, but on this matter our opinions differ.

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Old December 1st, 2002, 10:32 PM   #12
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Brian,

That is why I started the post with "correct me if I'm wrong". I understood that there was a technical reason that linear polarizers did not work as effectively with DV cameras. Maybe I worded it incorrectly. If you have anymore to say on this issue I'd appreciate it you'd contact me directly via e-mail so the thread doesn't turn into another DV vs film debarcle.
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Old December 2nd, 2002, 01:46 AM   #13
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I personally prefer the Tiffen Water White UltraPol 4x4 filter. It is the best Polarizer you can find. I have both the standard version as well as the "warm" 812 version.

http://www.tiffen.com/camera_filters.htm

- don
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Old December 2nd, 2002, 02:06 AM   #14
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I own the 3 piece Canon filter kit for each lens I own and don't shoot outside without the polarizer. I shoot a lot of aircraft and can get a nice medium blue sky if I want it. One thing I've found is that I have to do a white balance after each adjustment of the filter or I get a purple sky, but no biggie.

I got bored one day and decided to stack 2 to 3 of the polarizers in bright sunlight and got a cool effect similar to the beach scene in the movie "Contact" (where she meets her father). The sky looked very dark, but most everything else was "moonlit". Old film trick but it looked cool.

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Old December 2nd, 2002, 04:24 AM   #15
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Adrian,
Your concern about the effects of the color splitting system is a real one at first view. There is indeed a theoretical risk of getting slight polarisation effects in the small spectral parts where the dichroics change from transparant into reflective (between red and green, and between geen and blue), but this problem is beeing solved by chosing the right angles and some other optimisations. Same problems had to be solved for LCD projectors using color splitting prisms..See e.g. http://www.ee.ust.hk/~eekwok/publications/2000/AO_2000_39_168.pdf . If your cam would have polarisation effects on its own, just think what would happen if you rotate your cam when pointing to the sky or any other reflective surface...
Greg,
Indeed you can play with 2 stacked polars as a (strong) "ND" filter (first one must be linear). And if the first one is a circular one (the other is of no importance) you can even change the color balance in the scene. This is an ilustration of the fact that the retarder used for "depolarization" in circulars doesn't depolarize but just creates two orthogonal linearly polarized components which energies are wavelenght dependent.
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