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polarizer + lcd = ?

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Viewing 8 posts - 1 through 8 (of 8 total)
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  • #594
    staplermofo
    Participant

    Hi. I was fooling around with some polarizers and my LCD when I noticed I could do this:

    There’s a linear polarizer on the camera blocking out light from the lcd, then a circular polarizer in my hand sneaking light in. What on earth is going on and how can I use this weirdness to my advantage?

    (sorry for the low quality, I’m tired, drunk and impatient)

    #5059
    stupido
    Participant

    Hi. I was fooling around with some polarizers and my LCD when I noticed I could do this:

    There’s a linear polarizer on the camera blocking out light from the lcd, then a circular polarizer in my hand sneaking light in. What on earth is going on and how can I use this weirdness to my advantage?

    (sorry for the low quality, I’m tired, drunk and impatient)

    From what I read, a cicular polarizer is a regualr polarizer plus a secondary layer to de-polarize the light. The light that reaches the camera is supposed to be evenly split between vertical and horizonally polarized light as not to mess with the filters.

    So what you are seeing is half the light from the LCD.

    Basically, you have rotated the cicular polarizer so that its aligned with the polarized light of the LCD. IE, its not blocking anything. Now, the second layer is changing the polarization of some of the light. Thats what gets through the linear polarizer. From my reading it should be half of the LCD approximately. Assuming a lot of crap.

    Probably the best example of how a circular polarizer works.

    #5060
    stupido
    Participant

    Quicker wat to think.

    LCD screens are polarized. Assume vertical.

    You have adjusted the circular polarized to vertical.
    It is not blocking any of the LCD light. The second layer
    divides the light so it is half vertically and half horizonally polarized.

    Now you you adjust the linear polarizer to horizonal. It blocks all of the normal LCD light. But half the light through the circular polarizer is now horizonal and makes it through the linear polarizer.

    #5061
    schnee
    Participant

    Wow, two clicks through Wikipedia and i get this:


    and this

    and a whole lot more.

    That’s a pretty interesting photo there, staplermofo. From what I remember from uni, stupido (betraying his namesake) has it right. The CPL in your hand converts the linearly polarized light from the LCD into circularly polarized light. The linear polarizer on your lens (a) filters all linear light from the LCD and (b) takes out half the circularly polarized light coming through the CPL, but half still comes through.

    A decent picture of a linear polarizer can be found on Wikipedia’s “polarizer” entry. The wire grid may seem oriented wrong, but it is actually correct.

    Be careful mounting your linear polarizer on your (D)SLR – the internal focusing and metering optics of the SLR don’t work well with linears (but do work just fine with CPLs).

    #5062
    staplermofo
    Participant

    Wow, two clicks through Wikipedia and i get this:


    and this

    and a whole lot more.

    Now it makes sense, thanks.

    Is there anything you guys don’t know?
    I’m always amazed.

    #5063
    woman_in_red_dress
    Participant

    i have a circular polarizer and can’t tell the difference between photos using it and photos not using it. Obviously the above photo is cool looking, but I only have one polarizer.

    what the heck is it for? (I got it in a set of filters, but there were no directions).

    #5064
    staplermofo
    Participant

    i have a circular polarizer and can’t tell the difference between photos using it and photos not using it. Obviously the above photo is cool looking, but I only have one polarizer.

    what the heck is it for? (I got it in a set of filters, but there were no directions).

    I’m not really the best one to talk about it, so here’s a simple little site explaining it as used on normal digital camera with ever so helpful side by side comparisons.
    http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/polarizer.html

    #5065
    woman_in_red_dress
    Participant

    thanks, staplermofo!

    that site helped a lot!

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