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Thread: UWA and Vignetting

  1. #1

    Default UWA and Vignetting

    Hi, I'm a newbie in DSLR and this is a newbie question...

    I've read that when using a UWA lens (eg, Canon 10-22), adding a polarizer will cause vignetting or something like uneven polarization. In the market there are normal polarizer and slim profile polarizer (eg, Hoya "slim frame" CIR-PL or B+W CPL MRC "Slim"). Would using a slim profile polarizer avoid vignetting? But what about "uneven polarization" and btw, what is "uneven polarization"?

    One usually use UWA lens for wide landscape capture and on a bright sunny day using a CPL is preferred but wouldn't it be a shame if a CPL cannot be used on a UWA lens in this case?

    Anyone has any such experience and photo to share on the problem encountered using CPL on a UWA lens? Esp on "uneven polarizatoin" as vignetting is easy to tell.

    Thanks very much!

  2. #2
    Moderator daredevil123's Avatar
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    Default Re: UWA and Vignetting

    Quote Originally Posted by netuse38 View Post
    Hi, I'm a newbie in DSLR and this is a newbie question...

    I've read that when using a UWA lens (eg, Canon 10-22), adding a polarizer will cause vignetting or something like uneven polarization. In the market there are normal polarizer and slim profile polarizer (eg, Hoya "slim frame" CIR-PL or B+W CPL MRC "Slim"). Would using a slim profile polarizer avoid vignetting? But what about "uneven polarization" and btw, what is "uneven polarization"?

    One usually use UWA lens for wide landscape capture and on a bright sunny day using a CPL is preferred but wouldn't it be a shame if a CPL cannot be used on a UWA lens in this case?

    Anyone has any such experience and photo to share on the problem encountered using CPL on a UWA lens? Esp on "uneven polarizatoin" as vignetting is easy to tell.

    Thanks very much!
    You need to understand how a polarizer works. A CPL will filter out sun rays in a certain wave direction. Problem with UWA is that the angle of view is so wide that light rays in the captured frame are in actually fact from a wide range of directions. So certain parts of the frame will be polarized more than other parts of the frame. This will give rise to uneven polarization. This is just simple physics. The effect will be, some parts of the sky in the frame will be bluer than the other parts of the sky.

    Here is an example of how it looks like: http://static.photo.net/attachments/...5-24751284.jpg

    a slim CPL will most likely not vignette with a UWA, as lens manufacturers usually account for at least a filter attached to the end of the lens when designing it. And please do not stack the CPL over the UV/protector filter, that is very bad practice. When using a CPL, remove the UV/protector first, then put the CPL on.
    Last edited by daredevil123; 28th July 2010 at 02:27 PM.

  3. #3

    Default Re: UWA and Vignetting

    Thanks daredevil123 for the prompt reply.

    So I get it that they won't possibly be vignette using a slim CPM with a UWA lens, but the biggest problem would be uneven polarization.

    But then there will always be uneven polarization in any case, be it with a UWA lens or others. Is it just that the effect is less pronounce with others lens than a UWA lens since a UWA lens is capturing a much "wider area" of different arrays of light?

    So nothing we can do as far as polarization is concerned, if we are shooting a wide landscape on a sunny day?

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    Moderator daredevil123's Avatar
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    Default Re: UWA and Vignetting

    Quote Originally Posted by netuse38 View Post
    Thanks daredevil123 for the prompt reply.

    So I get it that they won't possibly be vignette using a slim CPM with a UWA lens, but the biggest problem would be uneven polarization.

    But then there will always be uneven polarization in any case, be it with a UWA lens or others. Is it just that the effect is less pronounce with others lens than a UWA lens since a UWA lens is capturing a much "wider area" of different arrays of light?

    So nothing we can do as far as polarization is concerned, if we are shooting a wide landscape on a sunny day?
    CPL filter rays in a specific range of directions. Just that UWA is so wide that the UWA range is much wider than what a CPL can handle. CPLs are not made equal too. Some will give uneven polarization with even 17mm focal lengths (on crop sensor). Some are ok. The one I choose to use is Kenko Pro1D wide-band CPL. But as "wide-band" as it is, it will give uneven polarization with UWA from around 13-14mm and below, on my lens and camera.

    Yes CPL is not very useful on UWA. If all you want to do is to make the sky darker and bluer, you can use a GND instead.
    Last edited by daredevil123; 28th July 2010 at 02:44 PM.

  5. #5

    Default Re: UWA and Vignetting

    Quote Originally Posted by daredevil123 View Post
    CPL filter rays in a specific range of directions. Just that UWA is so wide that the UWA range is much wider than what a CPL can handle. CPLs are not made equal too. Some will give uneven polarization with even 17mm focal lengths (on crop sensor). Some are ok. The one I choose to use is Kenko Pro1D wide-band CPL. But as "wide-band" as it is, it will give uneven polarization with UWA from around 13-14mm and below, on my lens and camera.

    Yes CPL is not very useful on UWA. If all you want to do is to make the sky darker and bluer, you can use a GND instead.
    This is probably a stupid question. So if CPL fails, could a ND filter on a UWA lens make the colour tune richer (that acts somewhat like a CPL does to non UWA lens) on a sunny day? No right?

  6. #6

    Default Re: UWA and Vignetting

    Quote Originally Posted by netuse38 View Post
    This is probably a stupid question. So if CPL fails, could a ND filter on a UWA lens make the colour tune richer (that acts somewhat like a CPL does to non UWA lens) on a sunny day? No right?
    Hmm.. nope.

    ND simply cuts your exposure (amount of light getting to your lens & sensor). I think what you might prefer is a GND, that only blocks a portion of the image (i.e. the sky).
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    Moderator Octarine's Avatar
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    Default Re: UWA and Vignetting

    Quote Originally Posted by netuse38 View Post
    This is probably a stupid question. So if CPL fails, could a ND filter on a UWA lens make the colour tune richer (that acts somewhat like a CPL does to non UWA lens) on a sunny day? No right?
    No, a CPL filters selected portions of the light (those that cause haze and / or those portions coming from reflections). ND filters are 'blind' in that regard, they just reduce everything that hits the glass. The effect of a CPL cannot be mimicked with ND filters.
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    Default Re: UWA and Vignetting

    Quote Originally Posted by Aimevous View Post
    Hmm.. nope.

    ND simply cuts your exposure (amount of light getting to your lens & sensor). I think what you might prefer is a GND, that only blocks a portion of the image (i.e. the sky).
    Like what Octarine mentioned, GND just darkens part of the frame. That's all.

  9. #9

    Default Re: UWA and Vignetting

    Thanks everyone for the enlightenment


    Will google more about uneven polarization and choice of CPL

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