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Thread: Which do you calculate first? Bellows factor or filter factor? Does it matter? Recipr

  1. #11

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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    Quote Originally Posted by Bob Salomon View Post
    I believe he meant the exposure correction for the filter, not what the factor is.
    I know, Bob. It was just a way to tell him that correct thinking is a better way to get correct answers.

  2. #12

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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    If you meter through the filter with a spot meter then all you need to do is measure the extension to see if there is any bellows to factor in. L

  3. #13
    Kleiny41's Avatar
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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    Quote Originally Posted by Luis-F-S View Post
    If you meter through the filter with a spot meter then all you need to do is measure the extension to see if there is any bellows to factor in. L
    Thanks, Luis!! Thanks, Everyone!

    (He is a she- not that it matters).

  4. #14

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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    Quote Originally Posted by Luis-F-S View Post
    If you meter through the filter with a spot meter then all you need to do is measure the extension to see if there is any bellows to factor in. L
    Those who are familiar with my posts know I'm an advocate of metering through filters (with appropriate testing and compensation) for general photography.

    However, I certainly would not meter through the filters for achieving color-separation negatives; this system needs careful calibration and the filter factors need to be determined by testing. Metering through the filters, especially if there are highly-color-saturated subjects (flowers) in the scene will lead to exposure errors. Apply the filter factors you know to be correct for your trichrome process.

    To the original question: Bellows extension and filter factors can be figured in any order; it's the total of the two that's important. That said, it is useful to have a worksheet and a consistent workflow. My exposure records start with basic metered exposure and then go to filter factor which is multiplied by the bellows extension factor to arrive at a total factor. From this, an adjusted exposure is figured, which is then adjusted for reciprocity failure (from my tables) if needed. A final "exposure given" field shows the actual exposure.

    Note that I use real exposure factors (not stops-to-change), which are multiplied to get a total factor. If you use the stops-to-change method, then just add the number of stops adjustment from filter and bellows extension. Note also that reciprocity failure adjustment always gets figured last, after all the other adjustments have been made.

    Hope this helps,

    Doremus

  5. #15
    ic-racer's Avatar
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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    Each equation results in a negative number. Remembering the rules of addition of negative numbers, one can flip the order of the two individual calculations without consequence.

    So:

    Filter Factor: -2
    Bellows Factor: -1.4

    Results:

    (-2) + (-1.4) = (-1.4) + (-2) = -3.4

  6. #16

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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    As far as making the aperture adjustments, the two corrections are additive. It would make no difference which adjustment was made to the aperture first.

  7. #17

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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    Quote Originally Posted by neil poulsen View Post
    As far as making the aperture adjustments, the two corrections are additive. It would make no difference which adjustment was made to the aperture first.
    ... shutter speed adjustments too, until you get to the point where reciprocity failure needs to be taken into account.

  8. #18
    tgtaylor's Avatar
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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    Many moons back I metered through the filter for the correction and the slide came back grossly underexposed. Ever since then I used the manufacturers value and never had a problem again.

    Thomas

  9. #19

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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    I'mma guess

    figure out the exposure with the filter.. then toss the bellows on top of that

    my thinking is find what the light is coming out the back of your lens (measured exp + filter factor)... and from there.. subtract bellows monkeysnot and voila..

  10. #20
    Huub
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    Re: Which do you calculate first? Bellows factor or filter factor? Does it matter? Re

    I would be very carefull measuring through a filter with a spot meter. My Gossen Spotmaster for instance is way off when measuring through a red filter. Such a thing would only work when the spectral sensitivity of the meter more or less matches that of our eyes and of the film.

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