How to Determine The Useful Longest Exposure Time Of A Digital Camera/Back

Discussion in 'Digital Photography' started by Einst Stein, May 1, 2006.

  1. Einst Stein

    Einst Stein Guest

    How do you determine the useful longest exposure time with your digital
    camera or the digital back?

    With films, I check the color shift and dynamic range to decide that.
    With the digital camera, I assume the color shift and the dynamic range
    can be somewhat compensated (within the reaonable range?), but the dark
    noise associated with the electroinc sensor due to the long exposure is
    much more difficult to handle.

    Does the professional digital photographers have any rule of thumb?
    What's the useful longest exposure time?
    Einst Stein, May 1, 2006
    #1
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  2. Einst Stein <> wrote:
    : How do you determine the useful longest exposure time with your digital
    : camera or the digital back?

    : With films, I check the color shift and dynamic range to decide that.
    : With the digital camera, I assume the color shift and the dynamic range
    : can be somewhat compensated (within the reaonable range?), but the dark
    : noise associated with the electroinc sensor due to the long exposure is
    : much more difficult to handle.

    : Does the professional digital photographers have any rule of thumb?
    : What's the useful longest exposure time?

    I'm not a pro but I expect the answer to be "it depends". One factor is
    what you consider a long exposure. If you are talking a 1/10th second
    exposure due to low light outdoors exposure, if you take all required
    steps to reduce relative motion between the camera and the subject, the
    long exposure shouldn't be a factor.

    A second factor is why are you using long exposure. If the reason is
    because you are using it for artistic uses (such as bluring out
    pedestrians in archetectural photography) or due to difficult lighting
    conditions (such as fireworks or night lightning photography) some level
    of inaccurate rendition will be forgiven by the viewer due to the "wow"
    factor of the subject. There will still be a logical limit of just how far
    you can push it, but this would vary from camera manufacturer as well as
    from individual camera to camera. This last part will have to be a
    personal determination you will have to make after experimentation with
    your specific equipment.

    One last factor is what use you intend. If this image is intended to be a
    portrait photograph but you don't want to use a flash and so you are using
    long exposure to compensate, get a flash. :) If you are hopeing to make
    poster prints or use the images in a major gallery show, the rendition
    accuracy requirement would be much higher than if you just want to print
    some 8x10s for hanging on your livingroom wall.

    Now for some practical experiences to give you a benchmark. As I said I am
    not a pro and I rarely intend to make money from my photos so I am not as
    picky as others. But I am not uncomfortable using ND filters to make a 30
    second exposure in which anything moving (cars, foot traffic, etc) blur
    into near invisibility when shooting buildings or monuments that would
    otherwise have a potentially distracting crowd of people around my
    subject. I have also done a few fireworks shots with a manual shutter that
    have been in the range of 30 to 45 seconds. Slight color shifts or such
    effects of an extreem long exposure are not overly noticeable or may even
    slightly enhance the result. I have even done a few "special effects"
    shots when I locked the shutter open for several min in a room in near
    total darkness while I "painted" with a light source in space. Some of
    these have gone on for a couple of min. The "how'd he do that" factor of
    glowing figures and words hanging in thin air completely disguises any
    effects of the long exposure.

    So my best advice is try various things out and see what pleases you. The
    only one that can make that decision is you.

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
    Randy Berbaum, May 1, 2006
    #2
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  3. Einst Stein

    Ron Hunter Guest

    Re: How to Determine The Useful Longest Exposure Time Of A DigitalCamera/Back

    Einst Stein wrote:
    > How do you determine the useful longest exposure time with your digital
    > camera or the digital back?
    >
    > With films, I check the color shift and dynamic range to decide that.
    > With the digital camera, I assume the color shift and the dynamic range
    > can be somewhat compensated (within the reaonable range?), but the dark
    > noise associated with the electroinc sensor due to the long exposure is
    > much more difficult to handle.
    >
    > Does the professional digital photographers have any rule of thumb?
    > What's the useful longest exposure time?
    >

    One aspect to consider is that with digital cameras the temperature at
    which the sensor captures the image can make a dramatic difference in
    the quality of the image at any given light level/exposure time.
    The difference is more pronounced, and at higher temperatures than the
    effect on film.
    Ron Hunter, May 1, 2006
    #3
  4. Einst Stein

    Pete D Guest

    "Einst Stein" <> wrote in message
    news:...
    > How do you determine the useful longest exposure time with your digital
    > camera or the digital back?
    >
    > With films, I check the color shift and dynamic range to decide that.
    > With the digital camera, I assume the color shift and the dynamic range
    > can be somewhat compensated (within the reaonable range?), but the dark
    > noise associated with the electroinc sensor due to the long exposure is
    > much more difficult to handle.
    >
    > Does the professional digital photographers have any rule of thumb?
    > What's the useful longest exposure time?
    >

    Given that the better cameras will have features such as dark frame
    subtracion it will depend how long you want to wait, given that it will
    double the length of your exposure,. How long do you want?
    Pete D, May 1, 2006
    #4
  5. Einst Stein

    Charles Guest

    On 30 Apr 2006 22:19:08 -0700, "Einst Stein" <>
    wrote:

    >How do you determine the useful longest exposure time with your digital
    >camera or the digital back?
    >
    >With films, I check the color shift and dynamic range to decide that.
    >With the digital camera, I assume the color shift and the dynamic range
    >can be somewhat compensated (within the reaonable range?), but the dark
    >noise associated with the electroinc sensor due to the long exposure is
    >much more difficult to handle.
    >
    >Does the professional digital photographers have any rule of thumb?
    >What's the useful longest exposure time?



    In the astro group they talk about using the Canon D300 routinely for
    5 minute exposures. I haven't done it, just read about it.
    Charles, May 1, 2006
    #5
  6. Einst Stein

    Pete D Guest

    "Charles" <> wrote in message
    news:...
    > On 30 Apr 2006 22:19:08 -0700, "Einst Stein" <>
    > wrote:
    >
    >>How do you determine the useful longest exposure time with your digital
    >>camera or the digital back?
    >>
    >>With films, I check the color shift and dynamic range to decide that.
    >>With the digital camera, I assume the color shift and the dynamic range
    >>can be somewhat compensated (within the reaonable range?), but the dark
    >>noise associated with the electroinc sensor due to the long exposure is
    >>much more difficult to handle.
    >>
    >>Does the professional digital photographers have any rule of thumb?
    >>What's the useful longest exposure time?

    >
    >
    > In the astro group they talk about using the Canon D300 routinely for
    > 5 minute exposures. I haven't done it, just read about it.


    I have read of the Pentax Ds's doing 40 minutes using DFS.
    Pete D, May 1, 2006
    #6
  7. Re: How to Determine The Useful Longest Exposure Time Of A DigitalCamera/Back

    Einst Stein wrote:

    > How do you determine the useful longest exposure time with your digital
    > camera or the digital back?
    >
    > With films, I check the color shift and dynamic range to decide that.
    > With the digital camera, I assume the color shift and the dynamic range
    > can be somewhat compensated (within the reaonable range?), but the dark
    > noise associated with the electroinc sensor due to the long exposure is
    > much more difficult to handle.
    >
    > Does the professional digital photographers have any rule of thumb?
    > What's the useful longest exposure time?
    >


    The noise in a good digital camera image is well modeled with the equation:

    N = (P + r^2 + t^2)^1/2,

    where N = total noise in electrons, P = number of photons
    converted to electrons, r = read noise in electrons,
    and t = thermal noise in electrons. The value if t increases
    with time and temperature, and varies from camera to camera.
    The signal is P, so signal-to-noise ratio is S/N = P/N
    Reference:

    Night and Low Light Photography with Digital Cameras
    http://www.clarkvision.com/photoinfo/night.and.low.light.photography

    You can calibrate your camera and measure the camera gain in
    photoelectrons/DN (the digital number in the image), measure the
    read noise, and thermal noise for use in the above equation.
    Example:

    Procedures for Evaluating Digital Camera Noise and Full
    Well Capacities; Canon 1D Mark II Analysis
    http://www.clarkvision.com/imagedetail/evaluation-1d2

    In general, low light work with a digital camera can produce
    much better images than with film. You can go fainter and
    have less noise than any film image ever could, but the
    work flow is different. Because of the thermal noise, exposure
    times are limited (the limit depends on the camera). Some
    cameras can go 30 minutes or more, but you will not get your best
    image at 30 minutes. You'll do better by taking several shorter
    exposures and adding them to get a total exposure time.
    This page shows some of the increases (see also the first low
    light photography page):

    Astrophotography Signal-to-Noise with a Canon 10D Camera
    http://www.clarkvision.com/astro/canon-10d-signal-to-noise

    Generally, DSLRs have low noise and can take the longest low light
    exposures.

    Roger
    Roger N. Clark (change username to rnclark), May 1, 2006
    #7
  8. Einst Stein

    Ian Anderson Guest

    Dark field subtraction aside, there are other problems lurking.
    I recently observed amplifier noise creating objectionable
    artifacts inside 10 minutes on a 300D. Fortunately the effects are a
    slight pink haze at one end of the field and can be cropped. It is also
    beneficial to take multiple exposures and stack (add) the images.

    Regards
    Ian

    On Mon, 01 May 2006 18:38:52 +1000, Pete D wrote:

    >
    > "Einst Stein" <> wrote in message
    > news:...
    >> How do you determine the useful longest exposure time with your digital
    >> camera or the digital back?
    >>
    >> With films, I check the color shift and dynamic range to decide that.
    >> With the digital camera, I assume the color shift and the dynamic range
    >> can be somewhat compensated (within the reaonable range?), but the dark
    >> noise associated with the electroinc sensor due to the long exposure is
    >> much more difficult to handle.
    >>
    >> Does the professional digital photographers have any rule of thumb?
    >> What's the useful longest exposure time?
    >>

    > Given that the better cameras will have features such as dark frame
    > subtracion it will depend how long you want to wait, given that it will
    > double the length of your exposure,. How long do you want?
    Ian Anderson, May 1, 2006
    #8
  9. Re: How to Determine The Useful Longest Exposure Time Of A DigitalCamera/Back

    Einst Stein wrote:

    >
    > Does the professional digital photographers have any rule of thumb?
    > What's the useful longest exposure time?
    >

    It's really all relative.....

    --
    John McWilliams
    John McWilliams, May 2, 2006
    #9
  10. Einst Stein

    Pete D Guest

    I have used Registrax for stacking but don't have a great need really.

    "Ian Anderson" <> wrote in message
    news:p...
    > Dark field subtraction aside, there are other problems lurking.
    > I recently observed amplifier noise creating objectionable
    > artifacts inside 10 minutes on a 300D. Fortunately the effects are a
    > slight pink haze at one end of the field and can be cropped. It is also
    > beneficial to take multiple exposures and stack (add) the images.
    >
    > Regards
    > Ian
    >
    > On Mon, 01 May 2006 18:38:52 +1000, Pete D wrote:
    >
    >>
    >> "Einst Stein" <> wrote in message
    >> news:...
    >>> How do you determine the useful longest exposure time with your digital
    >>> camera or the digital back?
    >>>
    >>> With films, I check the color shift and dynamic range to decide that.
    >>> With the digital camera, I assume the color shift and the dynamic range
    >>> can be somewhat compensated (within the reaonable range?), but the dark
    >>> noise associated with the electroinc sensor due to the long exposure is
    >>> much more difficult to handle.
    >>>
    >>> Does the professional digital photographers have any rule of thumb?
    >>> What's the useful longest exposure time?
    >>>

    >> Given that the better cameras will have features such as dark frame
    >> subtracion it will depend how long you want to wait, given that it will
    >> double the length of your exposure,. How long do you want?

    >
    Pete D, May 2, 2006
    #10
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