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  1. #71
    Thomas Bertilsson's Avatar
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    Whatever, man. You win, because I suck.
    "Often moments come looking for us". - Robert Frank

    "Make good art!" - Neil Gaiman

    "...the heart and mind are the true lens of the camera". - Yousuf Karsh

  2. #72
    percepts's Avatar
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    I didn't know I was in a competition.

  3. #73

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    [QUOTES=Ed Sukach;416477]

    "I know that the intensity of the light that
    reaches the film will determine the time of the exposure."

    I've no problem with that.

    "It is when the TIME itself becomes
    inordinately long that reciprocity comes into play."

    Long indicated exposures do need a correction
    factor applied.

    "Is there any (at all - no matter how little) reciprocity
    error / effect between the EV9 given as 1 second @ f/22
    and the EV9 as 1/60 second @ f/2.8? The total amount of
    light that reaches the film will be equal - only the
    time will be different."

    For most films a reciprocity correction will need be
    made at 1 second. Exposure time AND THE LEVEL OF
    ILLUMINATION at the film plane have changed. The
    level at f/22 is 1/64 that at f/2.8.

    "If so, what correction in terms of EV would be appropriate?"

    I use the indicated exposure time then apply the correction
    factor supplied with the film. I suppose a meter could be
    programed to read out a corrected time. Dan

  4. #74
    Photo Engineer's Avatar
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    Dan;

    HIRF takes place if the time is extremely short, as in very high intensity short duration strobe or the like.

    PE

  5. #75
    gainer's Avatar
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    Quote Originally Posted by Ed Sukach View Post
    Inescapable logic! A "straight line on log-log (are you sure you don't mean "deci-log"?) paper. Uh .. yeah .. but in real time .. it isn't a straight line ... but a logarithmic curve.
    Hopefully I won't have to revert to explaining logarithms here ...



    I know that the intensity of the light that reaches the film will determine the time of the exposure. I've known that for some .... Hah!! You thought you'd catch me admitting my age!. Well - a lot longer than I haven't known that.
    It is when the TIME itself becomes inordinately long that reciprocity comes into play.

    I tried that web address - unfortunately, it doesn't work. I have the Unblinking Eye bookmarked somewhere ... I'll give that a try - once I get some sleep.]
    ED,
    www.unblinkingeye.com should work. The title of the article there is "LIRF is Lurking at Your F-Stop". If you search for "LIRF" on the unblinkineye site, you should find it.

    The expression of LIRF correction as a straight line on log paper was determined by curve-fitting actual data, not as a logical theory. It makes no difference whether the log has the base 10 or 2 or 2.71828 the curve shape will be the same. The fact that the slope of the line, for practical use, is 1.62 for all films I had data for means that all you need to know about any given film is the time to be added when the measured time is 1 second, or for that matter, any other time. You can the draw a line through that point with a rise of 1.62 inches, centimeters, miles or kilometers and a unit run in corresponding units.

    One thing you will notice about logarithms is that there is no zero. The number whose log is zero is not zero but minus infinity. The logarithm of 0 is 1.0 in any base.

    When you use graph paper with a logarithmic scale, you are plotting time to be added against measured time, not their logarithms. It is not easy to get log-log paper these days, and if you cannot get it you can plot log vs log. The line will still be straight. I wrote a program to make my own log-log and semi-log graph papers. I can furnish a CD to set up that program on any version of Windows for the cost of reproduction and shipping.

    [My original question wasn't answered ... What correction would/ could be made in terms of EV? An example:

    To the Hasselblad lenses ... EV9 is 1 second @ f/22; and 1/8 second @f/8; and 1/60 second @ f/2.8. My exposure meter tells me I need EV9. Is there any (at all - no matter how little) reciprocity error / effect between the EV9 given as 1 second @ f/22 and the EV9 as 1/60 second @ f/2.8? The total amount of light that reaches the film will be equal - only the time will be different.

    If so, what correction in terms of EV would be appropriate?
    Any given EV can result in a wide range of f-stop and time combinations. There is no direct mathematical link between EV and LIRF. If you want a direct link between what your meter reads and the time to be added to the exposure time it calculates, you will have to compute the foot or meter candles of light that the meter is seeing, and will have to know the exposure time corresponding to some value of light intensity. Some meters have a table or scale that allows converting or reading directly the meter-candle value. It is not a direct, easily obtained conversion of EV to LIRF correction.
    Gadget Gainer

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