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Thread: Polarise or ND

  1. #1

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    Polarise or ND

    G'day, it's been a while since my last post, and I am probably repeating somebody else's question and I apologise if that is the case but,
    What is the difference between a polarising filter and a neutral density filter?
    and what would be the typical uses for each?
    Peter

  2. #2
    Administrator Manfred M's Avatar
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    Re: Polarise or ND

    They are totally different beasts (although a polarizer does act as around a 2-stop ND), but that is related to how it wors.

    Starting with a ND - look at these as basic sunglasses for your camera; it just reduces the amount of light entering entering the lens, so lets you use a slower shutter speed or wider aperture for a given ISO value.

    A polarizer lets only light oriented in a particular direction through. Light is normally scattered and comes in at different directions. Think of a polarizer as alot of parallel slits that are very close together (in fact that is exactly what you do have). Only light waves that are aligned (i.e. same direction of the slits) can make it through them, everything else is reflected off it, so only a portion of the light gets through (hence my comment about it acting as around a 2-stop ND filter). The advantage of using these is that it reduces the amount of reflection off non-metallic surfaces and results in a very blue looking sky (by reducing the light reflected off dust particle and water vapour in the atmosphere; but only for light that comes in at an angle from the direction of the sun. Shoot with the sun directly in front of you or behind you, no effect; shoot with the sun at right angles to the camera lens, maximum effect).

  3. #3
    rpcrowe's Avatar
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    Re: Polarise or ND

    Manfred is totally correct. I'd like to add that the polarizing filter or CPL (most modern cameras need circular polarizers) will provide more saturated colors in foliage or rocks, penetrate haze because it will minimize reflections from the suspended particulates, penetrate water by reducing surface reflections and reduce/eliminate reflections from windows. The polarizer will also help, by darkening the sky, to equalize the exposure between sky and foreground.

    However, although the CPL is considered a necessary adjunct to landscape photography by many photographers, a good polarizer is expensive and a poor one will cause more problems than it solves.

    Some photographers have problems rotating the front element of the polarizer when using a deep lens hood. I tend to be able to rotate the element with the tip of my index finger

    Polarise or ND

    Finally, using a polarizer costs you about two stops of exposure which is not normally a problem outside on bright days but, can be a problem indoors if you forget to remove it. I have done that and regretted it. Heck, I have made just about every mistake in the book but, usually can learn enough from the mistake not to repeat it. It can also be a bit of a problem on low light overcast days and will not make much of a difference because no direct sunlight. I would not use one at night due to the light los and because I love reflections in night shots...
    Last edited by rpcrowe; 5th August 2013 at 07:24 PM.

  4. #4
    Shadowman's Avatar
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    Re: Polarise or ND

    Quote Originally Posted by Poider View Post
    G'day, it's been a while since my last post, and I am probably repeating somebody else's question and I apologise if that is the case but,
    What is the difference between a polarising filter and a neutral density filter?
    and what would be the typical uses for each?
    Peter
    The ND filter can be used to photograph backlit subjects and allows you to shoot longer exposures without overexposing the scene.

  5. #5
    carloshpvp's Avatar
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    Carlos Henrique

    Re: Polarise or ND

    Besides the valuable explanations from the colleagues above, you can find very useful information here: http://www.cambridgeincolour.com/tut...ns-filters.htm
    Last edited by carloshpvp; 5th August 2013 at 07:20 PM.

  6. #6

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    Re: Polarise or ND

    Thank you all for that.
    Very helpful
    Petr

  7. #7

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    Re: Polarise or ND

    Not mentioned by CiC and above is the use of the polarising filter in 3d viewing of projected images. If you project two images on top of each other, one through a filter organised vertically and the other with a horizontal filter and wear corresponding polarised glasses one eye will see one image and the other eye the other for the 3-D effect.

    Manfred's comment about slots reminds me of the Russian 3-D system where the screen was covered with fine wires so that when sitting in a 'correct' position each eye saw its own view of the image. Seating was very limited and not a commercial proposition.

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