Switching to D - How does ISO work?

Discussion in 'Digital Photography' started by yagfxgeek, Nov 13, 2003.

  1. yagfxgeek

    yagfxgeek Guest

    I have been using my trusty Nikon F2AS and about 15 or so lenses for
    it since about 1980. Being a big fan of Photoshop and seeing the
    quality of a number of digital cameras, I have decided to take the
    plunge and retire the trusty F2AS in leiu of a Nikon D100. Now, I
    know almost nothing about Digital photography other then the
    information that I have read on the net and the beautiful images I
    have seen this camera create.

    My question is this: Is the CCD rated at some specific ISO/ASA? Is
    that setting adjustable if it is? The D100 has shutter speeds and
    obviously my lenses have a speed or maximum aperature rating as well
    as having an aperature (with 2 exceptions of catadioptric lenses).
    Therefore exposures must be calculated based on the sensitivty or
    speed of the CCD.

    Any infor or links to sites that might discuss this would be GREATLY
    appreciated!

    TIA!

    Mike
     
    yagfxgeek, Nov 13, 2003
    #1
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  2. Have you looked at http://www.dpreview.com/reviews/nikond100/

    . Auto (200 - 1600) - enabled via custom func.
    . ISO 200
    . ISO 250
    . ISO 320
    . ISO 400
    . ISO 500
    . ISO 640
    . ISO 800
    . ISO 1000
    . ISO 1250
    . ISO 1600
    . HI-1 (~ISO 3200)
    . HI-2 (~ISO 6400)

    ISO in a digital camera is set by the gain of the amplifier before the
    analog to digital converter. High gain translates to high sensitivity and
    high ISO. Hope this helps.
     
    Charles Schuler, Nov 13, 2003
    #2
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  3. yagfxgeek

    Ken Alverson Guest

    The ISO is adjustable, but the adjustment is made by cranking up the signal
    amplifier, and the more amplification, the more noise. Treat it like your
    choice of film ISO and select the lowest one that lets you achieve the
    settings you want. The big benefit is that you can change it between each
    shot, instead of having to use up a whole roll before switching to a different
    speed.

    I think you'll find up to ISO 400 looks excellent, beyond that it starts to
    get noisy, but so does 800+ speed film.

    Ken
     
    Ken Alverson, Nov 13, 2003
    #3
  4. yagfxgeek

    Don Coon Guest

    ISO in digicams is simply the amount of amplfier gain applied to the signal
    coming from the sensor. In general, increasing the gain also increases the
    noise -- also known as digital grain. Most digicams are terrible at higher
    ISOs. The normal base ISO seems to be 100 but some start at 50.

    Look here for a review of the D100's ISO performance compared to a Canon
    D60:
    http://www.dpreview.com/reviews/nikond100/page16.asp

    Good Luck!
     
    Don Coon, Nov 13, 2003
    #4
  5. yagfxgeek

    Paolo Pizzi Guest

    Yes. ISO 200 (100 not available on the D100.)
    Yes, from 200 all the way up to 6400 (which
    Nikon oddly calls "High 2", "High 1" being 3200.)
    ....up to 1/4000.
     
    Paolo Pizzi, Nov 13, 2003
    #5
  6. Are you sure of that? Have you tryed testing by changing ONLY the
    ISO and comparing the output data?

    --
    Paul Repacholi 1 Crescent Rd.,
    +61 (08) 9257-1001 Kalamunda.
    West Australia 6076
    comp.os.vms,- The Older, Grumpier Slashdot
    Raw, Cooked or Well-done, it's all half baked.
    EPIC, The Architecture of the future, always has been, always will be.
     
    Paul Repacholi, Nov 13, 2003
    #6
  7. yagfxgeek

    Don Coon Guest

    Don Coon, Nov 14, 2003
    #7
  8. yagfxgeek

    jam Guest

    Mike,

    | My question is this: Is the CCD rated at some specific ISO/ASA? Is
    | that setting adjustable if it is? The D100 has shutter speeds and
    | obviously my lenses have a speed or maximum aperature rating as well
    | as having an aperature (with 2 exceptions of catadioptric lenses).
    | Therefore exposures must be calculated based on the sensitivty or
    | speed of the CCD.
    |
    | Any infor or links to sites that might discuss this would be GREATLY
    | appreciated!

    Ken Alverson put it succinctly, but I'll try to elaborate a bit.

    Yes, each CCD has certain base sensitivity measured in something like
    voltage per unit light input. (If Dave Martindale were around, he
    could supply accurate details.) Some are slightly more sensitive than
    others, depending on design features like sensel area and depth and
    substrate thickness, but the base photosensitivity of silicon brackets
    the variation. The tiny analog CCD output voltages must be amplified
    up to levels suitable for digitization, storage and display. Digital
    camera engineers work hard to match their amplification levels with
    ISO numbers so that their camera speeds match the expectations of
    photographers used to ISO speed calibrations long established on the
    film side. Thus, you can take a digital camera's current ISO setting
    as the effective speed of its CCD plus associated electronics. You may
    then work with aperture, shutter speed and your lenses as would with
    film of the same sensitivity. Of course, a camera set at ISO 100 may
    turn out to act more like ISO 80 under testing, but camera-film
    combinations show similar variations.

    So far, so good, but as others have pointed out, higher ISO invariably
    means higher image noise, and noise only superficially resembles film
    grain. Some cameras are less noisy than others at a given ISO, again
    due to differences in CCD and circuit designs. (You generally pay big
    $$$ for that.) For more details, see

    www.cliffshade.com/dpfwiw/exposure.htm#iso
     
    jam, Nov 14, 2003
    #8
  9. yagfxgeek

    JPS Guest

    In message <>,
    I may be wrong, but I've heard that the D100 only goes up to ISO 800,
    electrically, and gets the higher ISOs by under-exposing and multiplying
    the results. In that case, you may be better off shooting at ISO 800
    yourself and underexposing, to preserve more highlights.
    --
     
    JPS, Nov 14, 2003
    #9
  10. yagfxgeek

    JPS Guest

    In message <>,
    I thought that my Canon 10D had true ISO 1600, but I shot a very dark
    frame at ISOs 100 through 3200 and used a program that dumps the raw
    data untouched, and the ISO 1600 and 3200 had numbers that were double
    the numbers I was getting in 100 through 800. This leads me to conclude
    that ISOs 100 through 800 are true (consistent), ISO 1600 is 800 pushed
    one stop arithmetically (double the values out of the ADC), and ISO 3200
    is 1600 pushed one stop arithmetically.

    Now, I'm wondering if enabling "ISO expansion" to get the pseudo-3200
    also changes the 1600 from true 1600 to pushed 800. Another experiment
    to conduct. If that is true, I will turn off ISO expansion and push it
    myself when I want ISO 3200 (or more).
    --
     
    JPS, Nov 14, 2003
    #10
  11. yagfxgeek

    JPS Guest

    In message <[email protected]_s51>,
    No, they haven't.

    You would have to compare not only the output at various ISOs, but with
    various pushes and pulls as well, to determine what true (consistent)
    ISOs a camera has.
    --
     
    JPS, Nov 14, 2003
    #11
  12. yagfxgeek

    JPS Guest

    In message <[email protected]_s54>,
    Not exactly. Many cameras just cut the exposure and multiply the
    numbers output by the analog-to-digital converter for some of their
    higher ISOs.
    --
     
    JPS, Nov 14, 2003
    #12
  13. yagfxgeek

    yagfxgeek Guest

    Thanks - this is exactly what I was looking for. Did not mean to
    start an argument amongst you all tho :(
     
    yagfxgeek, Nov 16, 2003
    #13
  14. yagfxgeek

    jam Guest

    | Thanks - this is exactly what I was looking for. Did not mean to
    | start an argument amongst you all tho :(

    Don't worry, nearly every question here starts an argument. (Different
    levels of understanding and misunderstanding often clash.) We're used
    to it. Soon you will be, too.
     
    jam, Nov 16, 2003
    #14
  15. nearly every question here starts an argument.

    <grin> I prefer to think of them as deeply-felt discussions
    by passionate photographers possessed of varying levels
    of artistic and verbal skill.

    Stan
    yep and I loved Hyde Park in London
     
    Stanley Krute, Nov 16, 2003
    #15
  16. yagfxgeek

    JohnH Guest

    jam, thanks for that informative article. From another relative newbie!

    John
    On the 'Poco Loco' out of Deale, MD
     
    JohnH, Nov 16, 2003
    #16
  17. They give SN ratios for changing exposure. I will see if I
    can get my hands on a few bodies to run some tests on.

    If anyone wants to try, set up a grey patch, and run s set of shots
    with MANUAL exposure. Just change the `ISO', do NOT change anything
    else then compare the raw data for the shots.

    --
    Paul Repacholi 1 Crescent Rd.,
    +61 (08) 9257-1001 Kalamunda.
    West Australia 6076
    comp.os.vms,- The Older, Grumpier Slashdot
    Raw, Cooked or Well-done, it's all half baked.
    EPIC, The Architecture of the future, always has been, always will be.
     
    Paul Repacholi, Nov 16, 2003
    #17
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