the difference about ISO by different company

Discussion in 'Digital Photography' started by maTheMatic, Jul 6, 2006.

  1. maTheMatic

    maTheMatic Guest

    Hi,guys
    Is there some difference about measuring ISO among different company
    dc or model? or they all have almost the same sensitivity given the
    same ISO number? In my memory, there are some different method related
    canon products, but can't find it in their webpage now.

    ---
    regards
     
    maTheMatic, Jul 6, 2006
    #1
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  2. Well...there isn't supposed to be. ISO is an acronym for a standards setting
    organization. If there are variations they aren't doing their job. But, some
    camera are off a bit because manufacturers think that snapshooters will get
    a higher number of acceptable photos if they under or over expose....I
    forget which. (all from old memories...not neccessarily factual)

    --
    Thanks,
    Gene Palmiter
    (visit my photo gallery at http://palmiter.dotphoto.com)
    freebridge design group

    "maTheMatic" <> wrote in message
    news:...
    > Hi,guys
    > Is there some difference about measuring ISO among different company
    > dc or model? or they all have almost the same sensitivity given the
    > same ISO number? In my memory, there are some different method related
    > canon products, but can't find it in their webpage now.
    >
    > ---
    > regards
    >
     
    Gene Palmiter, Jul 6, 2006
    #2
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  3. "Gene Palmiter" <> wrote in message
    news:Q20rg.4474$0V1.3282@trndny06...
    > Well...there isn't supposed to be. ISO is an acronym for a standards
    > setting organization. If there are variations they aren't doing their job.
    > But, some camera are off a bit because manufacturers think that
    > snapshooters will get a higher number of acceptable photos if they under
    > or over expose....I forget which. (all from old memories...not
    > neccessarily factual)


    Agreed.

    Another problem is that it's almost impossible to compare, since all
    metering systems other than spot metering (used by someone who knows what
    they are doing) are essentially random guessing games.

    Dpreview claims that Canon is consistently more sensitive than the claimed
    ISO levels, but I really doubt it. There are ISO standard procedures for
    measuring ISO in digital cameras, and I really doubt that Phil is using
    them.

    David J. Littleboy
    Tokyo, Japan
     
    David J. Littleboy, Jul 6, 2006
    #3
  4. maTheMatic

    Steve Wolfe Guest

    > Is there some difference about measuring ISO among different company
    > dc or model? or they all have almost the same sensitivity given the
    > same ISO number? In my memory, there are some different method related
    > canon products, but can't find it in their webpage now.


    I think I know the web page that you are referring to. If it's the same
    one that I'm thinking of, the guy took an expensive, calibrated meter, took
    shots at different exposures, and calculated the actual ISO that the camera
    was using, and the Canon model was, in fact, using a higher ISO than the
    simple "100/200/400/etc/".

    Ah, this is it:

    http://www.imaging-resource.com/PRODS/E5D/E5DA13.HTM

    Scroll down to "ISO accuracy".

    The short version is that yes, the Canon 5D (and probably other models)
    are shooting at a higher ISO than indicated. Instead of
    50/100/200/400/800/1600/3200, it's closer to 64/125/250/500/1000/2000/4000/

    steve
     
    Steve Wolfe, Jul 6, 2006
    #4
  5. maTheMatic wrote:

    > Hi,guys
    > Is there some difference about measuring ISO among different company
    > dc or model? or they all have almost the same sensitivity given the
    > same ISO number? In my memory, there are some different method related
    > canon products, but can't find it in their webpage now.
    >
    > ---
    > regards
    >


    The light meter's response in a camera is defined by ISO standards,
    International Standard ISO 2720: Photography - General
    purpose photographic exposure meters (photoelectric
    type) - Guide to product specification. First edition 1974.

    The basic equation is::
    lux = 12.4 * pi * f/#2 / (R * t * exposure_time * ISO),
    where f/# is the f/number of the camera lens, exposure
    time is in seconds, ISO is the ISO speed, R = reflectance
    of the target, t = lens transmission, and pi = 3.14159.

    The problem is that the "constant, 12.4 in the above equation,
    is not a constant. Different manufacturers can use different
    numbers. I've seen references to numbers as high as about 15,
    and a little lower than 12. So there is almost a
    50% "slop factor" built into the definition.

    Reference:
    Digital Cameras: Counting Photons, Photometry, and Quantum Efficiency
    http://www.clarkvision.com/imagedetail/digital.photons.and.qe

    Roger
     
    Roger N. Clark (change username to rnclark), Jul 6, 2006
    #5
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