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Thread: Long Exposure calc when sun is going down

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    Long Exposure calc when sun is going down

    While I have sort of figured out exposure & compensation in good light, when the sun is going down & I'm into reciprocity, I often am "behind" it & underexpose.

    A typical scenario might be a few minutes before the sun sets on a cloudy day.
    I might have a metered exposure of 30 seconds and say a reciprocity compensation that get's me to a minute.
    In that minute, the light is decreasing.
    I have tried "guessing" but want to know if there's a more reliable method.

    I suppose I could push the film in processing depending on how much things changed over the exposure, but....
    I shoot mostly color, trans & neg but I think this would be the same either way

    Thanks

    Dan

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    Re: Long Exposure calc when sun is going down

    I built a compensating light meter once, which corrected for things like dusk, dawn, sun going behind a cloud, etc. I was having a heck of a time on partly cloudy days when making paper negatives which have little lattitude. It's basically a capacitor, photodiode, pot, and comparator, and worked really well, even for fill flash. It was pre-internet though so my notes are all on paper.
    Science is what we understand well enough to explain to a computer. Art is everything else we do.
    --A=B by Petkovšek et. al.

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    Re: Long Exposure calc when sun is going down

    Curious how you used this circuitry to control exposure.
    Thanks
    Dan

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    Re: Long Exposure calc when sun is going down

    Quote Originally Posted by dswiger View Post
    While I have sort of figured out exposure & compensation in good light, when the sun is going down & I'm into reciprocity, I often am "behind" it & underexpose.
    A typical scenario might be a few minutes before the sun sets on a cloudy day.
    I might have a metered exposure of 30 seconds and say a reciprocity compensation that get's me to a minute.
    In that minute, the light is decreasing.
    I have tried "guessing" but want to know if there's a more reliable method.
    Dan
    Just meter during your exposure at, say, 3/4-way through. If your reading is significantly different, extend your exposure to match. This should get you really close; the extra exposure at the beginning will be balanced by the decreasing exposure at the end. If you are consistently overexposing doing this, then try 1/2-way. You can fine tune even more if you want.

    Best,

    Doremus

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    Re: Long Exposure calc when sun is going down


  6. #6
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    Re: Long Exposure calc when sun is going down

    It wasn't linked to the camera, it just turned an LED off when it was time to close the shutter. So once you opened the shutter you pressed a button and the LED came on, and then the meter integrated the light until the LED turned off.
    Science is what we understand well enough to explain to a computer. Art is everything else we do.
    --A=B by Petkovšek et. al.

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