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  1. #1
    hortense's Avatar
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    Filter Factor Polarizers

    Estimates how many stops of increased exposure are required using a circular polarizer? I have no in-camera exposure meter.
    [FONT=Times New Roman]MAC[/FONT]

  2. #2
    Dave Parker's Avatar
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    Depending on the brand, I have seen anywhere from 1.75 to 3 stops, there should be a filter factor printed on the rim of the filter, what brand is it?

    Dave

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    I think that a filter factor of 2.5 (=1 1/3 stops) is typical.
    Jerold Harter MD

  4. #4
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    Jared is close to on. but a circular polarizer increases/decreases in effect when rotated. This can swing a half a stop one way or the other. just something to bear in mind. Try using a hand held meter and meter the filter that way. Might get you closer than guessing.
    Thank you.
    CWalrath
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  5. #5
    hortense's Avatar
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    Quote Originally Posted by Satinsnow
    Depending on the brand, I have seen anywhere from 1.75 to 3 stops, there should be a filter factor printed on the rim of the filter, what brand is it?
    Dave
    Thanks Dave . The rim IS marked in 1-stop increment (plus/minus up to 2-stops). Didn’t’ look at it! Thanks for your help!
    MAC
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  6. #6
    Ole
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    There is no difference in the filter facton between circular and linear polarisers.

    Checking the meter reading while rotating shows how much polarised light is being absorbed by the filter, so IMO it makes more sense to use a fixed factor. After all, you want the brigh reflections to be darker, don't you?

    A second way to use polarisers is just the opposite: to enhance reflections. When rotated so that the reflections are strongest that light goes straight through, the rest of the scene is still 2 1/3 stops darker.
    -- Ole Tjugen, Luddite Elitist
    Norway

  7. #7
    hortense's Avatar
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    Quote Originally Posted by flash19901
    ... Try using a hand held meter and meter the filter that way. Might get you closer than guessing.
    Flash - Sounds like you've done this. I'll give it a try.
    Thanks,
    MAC
    [FONT=Times New Roman]MAC[/FONT]

  8. #8
    hortense's Avatar
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    Quote Originally Posted by Ole
    There is no difference in the filter facton between circular and linear polarisers.

    Checking the meter reading while rotating shows how much polarised light is being absorbed by the filter, so IMO it makes more sense to use a fixed factor. After all, you want the brigh reflections to be darker, don't you?

    A second way to use polarisers is just the opposite: to enhance reflections. When rotated so that the reflections are strongest that light goes straight through, the rest of the scene is still 2 1/3 stops darker.
    Ole - This sounds good. Thanks, MAC.

    .. and ALL you guys ... truly a knowledge tank.
    [FONT=Times New Roman]MAC[/FONT]

  9. #9

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    Stupid question alert.
    I know the Polariser takes out reflections and darken the sky to a degree depending on angle to the sun etc. I also know that an incamera meter will give different exposures because of that but I though the filterfactor should be constant since those effects are desired and if using a handheld meter for incident metering it should result in the correct exposure of the ground.
    Am I totally wrong ?
    Cheers, Søren
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  10. #10
    Ole
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    Søren, you're totally right. See my answer above.
    -- Ole Tjugen, Luddite Elitist
    Norway

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