DX-code exposure latitude code clarification requested.

Discussion in '35mm Cameras' started by Alan Browne, Feb 12, 2004.

  1. Alan Browne

    Alan Browne Guest


    Shows the 'code' for the exposure latitude portion of the 135 format DX

    On a roll of Velvia, the most pesimistic case is selected by the code,
    eg, per the table in the link above +/- 1/2.

    Now the latitude of Velvia is at least two stops either way, possibly
    +/-2.5 ...

    So does the DX code for exposure latitude have an offset base? (eg: 1.5
    or 2 would seem to make sense).
    eg does the +/- 1/2 really mean +2 +1/2 to -2 -1/2 (+2.5 to -2.5)?

    Or is the code really meant to drive the program exposure mode s/w with
    an idea of how loose or tight the s/w should interpret the scene?

    One tidbit I found via Google suggests it merely helps the camera in
    program mode to determine if it can keep the shutter fast enough to
    avoid camera shake and still get a reasonable exposure. In this case,
    only the under exp side would be needed, so seems like a partial
    response at best.

    All replies apreciated.

    Alan Browne, Feb 12, 2004
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  2. Alan Browne

    Bill Tuthill Guest

    No the dynamic range of Velvia is +2/-2 or +/-2.5 if you prefer,
    but exposure latitude is not the same thing as dynamic range.
    For most normal scenes with brightness ranges of 4 stops or more,
    you could not expose Velvia 50 at EI 12 or EI 200 and still get
    acceptable results.

    That's what exposure latitude means: acceptable results at a
    given number of stops over and under. Most print films can
    easily handle +2/-2 and some more than that.
    Yes, but I don't know of any cameras that actually make use of it.
    Bill Tuthill, Feb 13, 2004
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  3. Alan Browne

    Alan Browne Guest

    No matter what tolerance "exposure latitude" they put on the DX-code,
    the exposure range will not change as you change the center (18% grey)
    point... , eg: if the exp. is set for 1/10 of a stop to overexpose, then
    that much more detail will appear in the shaddows, and that much more
    detail will be lost in the highlights. +/- 1/2 latitude means nothing.

    Exp. latitude DOES mean something for negative film, as you're going to
    make prints from it and you have a lot of latitude for correction. But
    for reversal it seems like a meaningless term.
    I now think that is its only purpose, eg: useless to anyone but P mode
    Alan Browne, Feb 15, 2004
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