How does ISO setting work?

Discussion in 'Digital SLR' started by David, Mar 5, 2010.

  1. David

    MikeWhy Guest

    ISO 1600 is 4 stops down from ISO 100, not 16 stops.
    Please check the numbers; I'm pretty sure you have part of that wrong.
    Stacking 8 exposures shot at (virtual) ISO 25600 might be what was intended.

    Hyphenated, versus simply smeared in the single longer exposure. No biggee.
    100 * 2^4 = 1600.
    100 * 2^8 = 25600.
    100 * 2^16 = 6553600.
     
    MikeWhy, Mar 11, 2010
    #41
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  2. David

    Martin Brown Guest

    Be interested to see an example of shadow banding at low ISO on the 7D -
    a fragment at full resolution PNG lossless compressed would do.

    Regards,
    Martin Brown
     
    Martin Brown, Mar 11, 2010
    #42
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  3. David

    Martin Brown Guest

    If you can find one of these OOC JPEGs I would be interested to take a
    look at it. My curiosity is peeked. The most obvious cause would be some
    kind of rounding error in the transfer function from RGB to YCC.

    Please send one to me privately at the odd looking reply to address.
    (no alterations needed it is valid when unmodified)

    Certain other well known leading packages have very similar faults
    although the damage is usually most annoying in highlights where clear
    chroma to luminance bands can appear in highlights.

    A green to magenta diagonal gradient put through the JPEG encode/decode
    cycle a few times is a very good test of rounding errors in the codec.
    any rounding errors and it will break up into chunky bars of colour.
    Unfortunate given that JPEG relies on 8x8 periodicity.
    I only have Canon Ixus P&S but I can't say I have ever had problems with
    their black point calibration. Its main attraction is always being with me.

    Regards,
    Martin Brown
     
    Martin Brown, Mar 12, 2010
    #43
  4. Doesn't Nikon black clamp its images? If so for a fair comparison the
    Canon images should be manually black clamped to the same extent.
     
    Chris Malcolm, Mar 12, 2010
    #44
  5. I said "clamping" rather than "clipping" but I may have used the wrong
    term. What I meant was I thought Nikon had decided on a black
    threshold below which they would simply make the pixels completely
    black. So the deepest shadows are perfectly black with no noise at
    all.
     
    Chris Malcolm, Mar 14, 2010
    #45
  6. And 4 stops is 1/16th of the exposure, so 16 shots at ISO1600 is the
    same exposure time as 1 shot at ISO100.

    You seem to be confusing stops with # of exposures.
    Correct and put another way this shows:
    2^1 (ie. 2) shots at ISO1600 is the same exposure time as one ISO800
    2^2 (ie. 4) shots at ISO1600 is the same exposure time as one ISO400
    2^3 (ie. 8) shots at ISO1600 is the same exposure time as one ISO200
    2^4 (ie. 16) shots at ISO1600 is the same exposure time as one ISO100
    So 256 exposures at ISO25600 will take the same time as one at ISO100.
    So 65536 exposures at ISO6553600 will take the same time as one at
    ISO100.
     
    Kennedy McEwen, Mar 14, 2010
    #46
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