Reciprocity failure in digital camers?

Discussion in 'Digital Photography' started by g@risky-biz.com, Sep 12, 2006.

  1. Guest

    I like to take night shots. I've had some success at it with my film
    SLRs, but there was always some voodoo involved; taking several shots
    on B, holding the shutter open for 2 seconds, 5 seconds, 10 seconds,
    etc.

    I just got a Kodak P880. I chose it mostly for the wide angle
    capability and the reasonable price. While on vacation in Montreal and
    Quebec City I got to experiment a bit with it. I have to say that the
    ability to view the night shots on the screen was a real blessing. It
    allowed me to fine-tune the exposure and be sure I got a decent shot.

    I have to say that sometimes (not all the time) it was almost too easy.
    In certain modes the auto-exposure will use shutter speeds up to 16
    seconds. It got the exposure pretty close to "right" a fair percentage
    of the time.

    That notwithstanding, I'm curious about reciprocity with digital
    sensors, if only to know what is going on a bit better. Is there a
    point at which doubling the exposure time doesn't produce a "one stop"
    change, as with film? Or makes a color change?

    I also did a litle experimenting with the ISO settings but not in a
    systematic way, I'm afraid. Assuming no camera shake, and a stationary
    subject (buildings, etc.), would you use a lower ISO and longer
    exposure or the other way around? I'm wondering which results in less
    noise.

    Greg Guarino
    , Sep 12, 2006
    #1
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  2. acl Guest

    wrote:
    > I like to take night shots. I've had some success at it with my film
    > SLRs, but there was always some voodoo involved; taking several shots
    > on B, holding the shutter open for 2 seconds, 5 seconds, 10 seconds,
    > etc.
    >
    > I just got a Kodak P880. I chose it mostly for the wide angle
    > capability and the reasonable price. While on vacation in Montreal and
    > Quebec City I got to experiment a bit with it. I have to say that the
    > ability to view the night shots on the screen was a real blessing. It
    > allowed me to fine-tune the exposure and be sure I got a decent shot.
    >
    > I have to say that sometimes (not all the time) it was almost too easy.
    > In certain modes the auto-exposure will use shutter speeds up to 16
    > seconds. It got the exposure pretty close to "right" a fair percentage
    > of the time.
    >
    > That notwithstanding, I'm curious about reciprocity with digital
    > sensors, if only to know what is going on a bit better. Is there a
    > point at which doubling the exposure time doesn't produce a "one stop"
    > change, as with film? Or makes a color change?


    No, there is no colour shift or loss of sensitivity. There is an
    increase of hot pixels; some cameras have a dark frame subtraction
    feature which eliminates them (by taking another exposure of the same
    length with the shutter closed immediately afterwards and subtracting
    that). This usually doubles the exposure time (since the second exposure
    is of the same length). Of course, you can simply not use this (I don't
    with my D200 for ISOs below 400 and shutter speeds up to about half a
    minute). Experiment!

    >
    > I also did a litle experimenting with the ISO settings but not in a
    > systematic way, I'm afraid. Assuming no camera shake, and a stationary
    > subject (buildings, etc.), would you use a lower ISO and longer
    > exposure or the other way around? I'm wondering which results in less
    > noise.


    As for this, I imagine it depends on the camera. Probably best to
    experiment with yours and decide based on that.
    acl, Sep 12, 2006
    #2
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  3. Matt Ion Guest

    wrote:

    > That notwithstanding, I'm curious about reciprocity with digital
    > sensors, if only to know what is going on a bit better. Is there a
    > point at which doubling the exposure time doesn't produce a "one stop"
    > change, as with film? Or makes a color change?


    Well, here are a couple examples:

    http://www.pbase.com/image/34152731

    "This is a long (almost 9 minutes) exposure that I took last night using only
    the light from the moon." - Annika1980 (circa Sept 2004)

    Here's one I took under moonlight as well:
    http://www.photosig.com/go/photos/view;jsessionid=ayxWb5sc9kDfz-oKI2?id=1716559

    > I also did a litle experimenting with the ISO settings but not in a
    > systematic way, I'm afraid. Assuming no camera shake, and a stationary
    > subject (buildings, etc.), would you use a lower ISO and longer
    > exposure or the other way around? I'm wondering which results in less
    > noise.


    Lower ISO will generally mean less noise, but remember it also needs a wider
    aperture for the same exposure time, which will lose some DOF, and that a longer
    exposure will eat up more batteries.
    Matt Ion, Sep 12, 2006
    #3
  4. Marvin Guest

    wrote:
    <snip>
    > That notwithstanding, I'm curious about reciprocity with digital
    > sensors, if only to know what is going on a bit better. Is there a
    > point at which doubling the exposure time doesn't produce a "one stop"
    > change, as with film? Or makes a color change?

    <snip>
    > Greg Guarino
    >


    The silver halide particles in film must absorb 2 photons
    within a short time interval for the particle to become a
    silver metal particle in development. That is the cause of
    reciprocity failure, and it does not happen with a digital
    sensor. When a sensor pixel has reached the point where it
    can't hold more charge, it is said to be saturated. Near
    there, doubling the exposure time will produce less of a
    change. Saturation also occurs with film. It is not
    reciprocity failure.
    Marvin, Sep 12, 2006
    #4
  5. Stormlady Guest

    <> wrote in message
    news:...
    >
    > I also did a litle experimenting with the ISO settings but not in a
    > systematic way, I'm afraid. Assuming no camera shake, and a stationary
    > subject (buildings, etc.), would you use a lower ISO and longer
    > exposure or the other way around? I'm wondering which results in less
    > noise.
    >
    > Greg Guarino
    >


    I have the Kodak P850 (for the zoom) and I have found that in certain shots,
    going over iso 200 produced a lot of noise, really an unreasonable amount.
    For example, we were at the fair with our daughter and she was on a ride,
    Trying to get the shot of her moving, boyfriend turned the iso up to 200 and
    the pictures are really pretty bad. Unusably bad because of the noise.
    That being said, I've taken pictures of other things at the higher iso and
    not gotten them so noisy, things that weren't moving as much.
    Stormlady, Sep 12, 2006
    #5
  6. Ron Baird Guest

    Greetings Greg,

    Glad to hear about the shots of Montreal. Great city and the P880 could
    capture most all scenes.

    You do not have to worry about reciprocity in digital, variations are
    accounted for in the camera. Reciprocity is really more related to film and
    some paper. With Film, if you use long exposures the sensitivity of the film
    is reduced slightly which can cause a shift in color. With a digital camera
    that problem is removed and most cameras can handle exposures of several
    seconds or longer.

    What you should consider is that low light or higher ISO settings in digital
    camera can yield an increase in 'noise' the digital equivalent of grain. You
    may want to get a good filter for it, or in your case improve on some shots
    with flash. The P20 can talk to your camera and would be an advantage.

    Talk to you soon,

    Ron Baird
    Eastman Kodak Company




    <> wrote in message
    news:...
    >I like to take night shots. I've had some success at it with my film
    > SLRs, but there was always some voodoo involved; taking several shots
    > on B, holding the shutter open for 2 seconds, 5 seconds, 10 seconds,
    > etc.
    >
    > I just got a Kodak P880. I chose it mostly for the wide angle
    > capability and the reasonable price. While on vacation in Montreal and
    > Quebec City I got to experiment a bit with it. I have to say that the
    > ability to view the night shots on the screen was a real blessing. It
    > allowed me to fine-tune the exposure and be sure I got a decent shot.
    >
    > I have to say that sometimes (not all the time) it was almost too easy.
    > In certain modes the auto-exposure will use shutter speeds up to 16
    > seconds. It got the exposure pretty close to "right" a fair percentage
    > of the time.
    >
    > That notwithstanding, I'm curious about reciprocity with digital
    > sensors, if only to know what is going on a bit better. Is there a
    > point at which doubling the exposure time doesn't produce a "one stop"
    > change, as with film? Or makes a color change?
    >
    > I also did a litle experimenting with the ISO settings but not in a
    > systematic way, I'm afraid. Assuming no camera shake, and a stationary
    > subject (buildings, etc.), would you use a lower ISO and longer
    > exposure or the other way around? I'm wondering which results in less
    > noise.
    >
    > Greg Guarino
    >
    Ron Baird, Sep 19, 2006
    #6
  7. Alan Meyer Guest

    Ron Baird wrote:
    > ...
    > What you should consider is that low light or higher ISO settings in digital
    > camera can yield an increase in 'noise' the digital equivalent of grain. You
    > may want to get a good filter for it, or in your case improve on some shots
    > with flash. The P20 can talk to your camera and would be an advantage.
    > ...


    I'm not an expert on this, but I hypothesize that the explanation
    for Ron's comment is as follows:

    A digital sensor accumulates charge (i.e., electrons) in each
    pixel position as a response to light falling on the sensor in that
    position.

    The sensor also accumulates charge in each pixel simply as
    a result of the random motion of electrons (due to heat,
    radiation, and perhaps other factors other than stimulation
    by light.)

    We see digital "noise" when the ratio of random charge becomes
    a significant percentage of the total charge in a pixel, causing
    the value of that pixel to have a noticeable random component
    to it.

    The sensor accumulates random charge as a function of time.
    The sensor is discharged just before the image is made, and
    read after the image is made.

    In bright light, the time between pre-image discharge and
    post-image reading is short, allowing little random charge
    to accumulate.

    In dim light the time is long, allowing more random charge
    to accumulate. Hence the extra noise in low light situations.

    Dark areas of an image are most subject to this because
    the random charge in all areas of the image is the same, but the
    dark areas have a higher percentage of random to light
    stimulated charge accumulation.

    The "filtering" that Ron talks about is the digital process of
    averaging adjacent pixels with similar values in order to
    eliminate differences that are due to random factors. But
    no filter, no matter how smart, can truly distinguish
    differences due to random charge as distinct from differences
    due to different amounts of light. It uses heuristic algorithms
    to make intelligent guesses, which are often but not always
    right. Hence there is always some loss of detail when
    aggressive noise filtering is performed.

    Alan
    Alan Meyer, Sep 19, 2006
    #7
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