shutter speed and exposure time

Discussion in 'Australia Photography' started by Don, Oct 25, 2003.

  1. Don

    Don Guest

    When playing around with a particular file in windows explorer I was able to
    read the exif data that included the following figures:

    exposure speed 1sec
    exposure time 1/6 sec

    I have always thought that you set your exposure by establishing the size of
    the aperture (ie F4) AND utilising the time the shutter stayed open (ie
    1/6th of a second). What is the exposure speed.

    Don, Oct 25, 2003
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  2. Don

    Ken Guest

    A total guess, but exposure "speed" = ISO? 1 being 100 not sure what the
    'sec' would indicate, assuming a bug?.

    What camera, your 10D?

    Ken, Oct 25, 2003
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  3. Don

    k Guest


    Exposure time, given in seconds (sec).
    Tag = 33434 (829A.H)
    Type = RATIONAL
    Count = 1

    Shutter speed. The unit is the APEX (Additive System of Photographic
    Exposure) setting (see Annex C).
    Tag = 37377 (9201.H)
    Type = SRATIONAL
    Count = 1

    The relation between the two values is given by the

    ShutterSpeedValue = -log_2( ExposureTime)

    (where log_2 denotes the logarithm of base 2).

    So one should have the following table:

    ShutterSpeedValue ExposureTime
    -3 8
    -2 4
    -1 2
    0 1
    1 1/2
    2 1/4
    3 1/8
    k, Oct 25, 2003
  4. Don

    Ubiquitous Guest

    Sounds overly complex, but still doesn't explain why speed of 1 sec = time
    of 1/6 sec.
    By that table, the time should have been 1/2 of s ec?
    Ubiquitous, Oct 26, 2003
  5. Don

    k Guest

    I'da thought so to, but that was the result of a quick google search (hence the
    referenced link) - maybe ISO has something to do with it. hmmm. at least now
    be both know that the seemingly contradictory figures of speed and time have
    some actual correlation, something I too did not know before

    k, Oct 26, 2003
  6. Don

    Don Guest

    I just get further confused. Yes, its with my 10D.

    Regards and thanks for the responses. I will post anything that comes close
    to answering

    Don, Oct 26, 2003
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