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  1. #1

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    How to open 1/3 stop with ISO dial.

    I've got a 1/3 stop filter compensation to work with. Not all my lenses have aperture stops of 1/3 and shutter speed is only full stops. So to make things easier, when using a handheld light meter, I thought I'd dial in the compensation with ISO on the camera.

    I've got 160 speed film. I leave the light meter at 160 ISO and set the ISO dial on the camera to 200 ISO. Is that right?
    Thanks,
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  2. #2
    Christopher Walrath's Avatar
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    What camera are you using. Would help to know.

    Keep it light.
    ChrisW
    Thank you.
    CWalrath
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  3. #3

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    Quote Originally Posted by kbrede View Post
    I've got a 1/3 stop filter compensation to work with. Not all my lenses have aperture stops of 1/3 and shutter speed is only full stops. So to make things easier, when using a handheld light meter, I thought I'd dial in the compensation with ISO on the camera.

    I've got 160 speed film. I leave the light meter at 160 ISO and set the ISO dial on the camera to 200 ISO. Is that right?
    Thanks,
    Wrong. To give 1/3 stop more exposure you need to set to 125 ISO.

  4. #4
    markbarendt's Avatar
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    Filters reduce exposure.

    Moving the meter's/camera's, EI/ISO setting, from 160 to 200 also reduces camera exposure, in this case by 1/3 stop.

    To offset a 1/3 stop filter's reduction in exposure move from a setting of 160 to 125 to add that exposure back in.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  5. #5
    Terry Christian's Avatar
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    E. van Hoegh is correct. Your filter blocks 1/3 stop of light, so you need to trick your camera into thinking the camera has slower film in it so that it'll let in more light. Opening your aperture to a lower f-stop number, or lengthening your shutter speed, will have the same effect.

  6. #6
    Bill Burk's Avatar
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    When factoring in filters, I set the EI for the film & filter factor combination on the handheld meter, (as pointed out for 160 and 1/3 stop filter factor, 125 is the answer).

    I set that on the handheld meter as ISO B and use that.

    I would leave the camera at 160, for example an SLR with through-the-lens metering would attempt to compensate anyway.

  7. #7

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    My understanding is that published filter factors are not always correct and can vary from mfg to mfg as well as with the color of the filter and the colors of the subject. It would be best to meter through the filter and without the filter to see the difference before making the adjustment if that degree of accuracy is important.

    http://www.jeffreyglasser.com/

  8. #8

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    Wait a minute. Are you metering with the camera's meter or the handheld meter?? Changing the ISO setting on the camera and then metering with the handheld set to 160 will compensate for nothing. If the camera has TTL metering, it will (as has been pointed out) automatically compensate for the filter factor

  9. #9

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    Quote Originally Posted by jeffreyg View Post
    My understanding is that published filter factors are not always correct and can vary from mfg to mfg as well as with the color of the filter and the colors of the subject. It would be best to meter through the filter and without the filter to see the difference before making the adjustment if that degree of accuracy is important.

    http://www.jeffreyglasser.com/
    This will work only if the meter cell and the film have identical spectral response, which is not often the case.

  10. #10
    ic-racer's Avatar
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    Quote Originally Posted by kbrede View Post
    Not all my lenses have aperture stops of 1/3 and shutter speed is only full stops.
    You can't make a 1/3 stop exposure adjustment with that camera.

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