Shutter Priority Vs. Aperture Priority Question

Discussion in 'Digital Photography' started by mutefan, Sep 13, 2006.

  1. mutefan

    mutefan Guest

    Last evening, I experimented with a new digital camera, taking
    photographs of changing maples leaves here in Northeast PA. It was
    dusk, and the annoying Autofocus blasted a flash at the trees. I hate
    the unnatural look of pictures illuminated by "flash light."

    Anyway, I was under the impression that opening the aperture would
    capture the low-light beauty, but every photo came out blurred (my
    aperture is 2.8 max). So for the heck of it, I kept lowering the
    shutter speed. At about 1/4 (whatever *that* means) to 1/25, I got the
    most incredible, atmospheric pictures of blackened branches at very
    close range, with the more distant colored leaves in a fantastic blur.
    The result was a quasi-ominous composition very...autumnal (and it's
    not even "high autumn" here).

    Anyway, I thought opening the aperture, not heightening the shutter
    speed, was the trick to capturing good low light pictures where the
    subject (here, unintended) was in focus. The depth of field in these
    nature pictures is terrible of course, but the crispness of the bare
    branches is great.

    So IS aperture priority best for low light pictures where you want a
    (near) subject in focus, or is it best for low light pictures where you
    want better depth of field?

    Thanks! (Oh, and I'd appreciate any site where I can find the digits
    and fractions associated with shutter speed explained.)
    mutefan, Sep 13, 2006
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  2. mutefan

    bugbear Guest

    Every photo you took has a shutter speed and an aperture.

    Conveniently, this will be recorded by most digital cameras
    as EXIF.

    Use the EXIF data in your photos (both the good and bad)
    to try to understand the effects of both, and how
    they interact.

    bugbear, Sep 13, 2006
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  3. mutefan

    Gadi Ben-Avi Guest

    A shutter speed of 1/4 means that the shutter is open for a quarter of a
    A shutter speed of 1/25 means that the shutter is open for a 25th of a
    second. which is 6.25 time faster than 1/4.
    This means that at the same apperture there will be 6.25 times less light
    for your sensor to work with.

    Gadi Ben-Avi, Sep 13, 2006
  4. Whether you use aperture priority or shutter priority, you are always
    using the computer to calculate exposure. Low light photography needs
    a certain combination of aperture and shutter speed. You do not NEED
    to select aperture priority to get proper exposure. The normal reason
    to select aperture priority is to control depth of field.

    With most cameras you can select a NO-FLASH setting and still use
    completely automatic or programmed exposure. The computer in the
    camera will select the appropriate exposure.

    In low light conditions, even with wide open aperture, the shutter
    speed is likely to be slow, and held-held cameras will exhibit blur
    from motion, that is sometimes hard to distinquish from blur due to
    defocus. In low light conditions without flash, a tripod becomes
    Don Stauffer in Minnesota, Sep 13, 2006
  5. mutefan

    Shawn Hirn Guest

    The smaller the aperture, the more shallow your depth of field becomes.
    With an aperture of 2.8, you are using a very narrow depth of field.
    Depth of field refers to the distance before and after the intended
    subject that remains in focus.

    Do a google search on "basic photography" and you'll find tons of
    information on this subject. The relationship between shutter speed,
    aperture (i.e., lens opening), and depth of field is covered in any
    basic photography book.
    Shawn Hirn, Sep 13, 2006
  6. To capture a subject in low light, you need to increase your exposure.
    This can be done by either opening the aperture -or- by moving to a
    slow shutter speed -or- by switching to a higher ISO rating. Each of
    these has possible disadvantages:

    - A wide aperture gives you narrow depth-of-field, so less of the
    picture will be in focus
    - A slow shutter speed is difficult or impossible to hand-hold, so you
    need a tripod. It also blurs any motion in the scene.
    - A high ISO rating introduces more noise into the image

    Often you combine these...for instance, in low light I've taken
    pictures with a wide aperture (f/1.8) and high ISO (1600 or 3200)
    because I didn't have a tripod, so I couldn't switch to a slow shutter

    For a typical low-light landscape shot, you'd probably use a low ISO
    (say 100-400),
    1/4 means a quarter-second (i.e. 0.25 seconds). 1/25 is a twenty-fifth
    of a second (0.04 seconds). Longer shutter speeds have three effects:
    - More light gets into the camera, so the picture is brighter (assuming
    the same aperture and ISO)
    - Things that are moving in the picture are more likely to be blurred
    - It is more important to hold your camera perfectly still (i.e. use a
    tripod), because camera shake is more likely to cause the entire
    picture to be blurred

    Note that when using some slower/longer shutter speeds, even with the
    camera on a tripod, it's quite easy to ruin the picture just by the
    amount of camera shake introduced by pushing the shutter button. Using
    the camera's self-timer or a remote control is recommended.
    The trick is simply to get the correct exposure, whether you do that by
    adjusting the shutter speed, aperture, or ISO. The exact approach you
    take depends on the situation and on the effect you want. A couple
    typical examples:

    - For landscape-type photos of stationary objects, use a small aperture
    (i.e. high f-number), slow shutter speed, low ISO, and tripod
    - For handheld shots in low light, use a large aperture (low f-number),
    fast shutter speed, and high ISO
    This is because the branches were in focus, and neither they nor the
    camera moved significantly while the shutter was open.
    Honestly, for low-light pictures, I tend to use manual mode. It's easy
    for the camera's meter to be confused, and even when it's not, it may
    be aiming for a lighter or darker exposure than what you want.
    My Canon camera gives shutter speeds in two ways.

    For fast shutter speeds, it simply displays an integer (4, 25, 60,
    1000, etc.) These are fractions of a second (1/4 second, 1/25 second,
    1/60 second, 1/1000 second). The larger the number displayed, the
    faster the shutter speed. Fast shutter speeds (like 1/1000 second) let
    a lot less light into the camera than slow shutter speeds (like 1/4

    As you move to slower shutter speeds, it switches to numbers with a "
    after them (0.5", 1", 2", 4", etc.) These are in seconds (half a
    second, one second, two seconds, four seconds). In this case, the
    larger the number, the SLOWER the shutter speed.

    So, there's a very important difference between a shutter speed of 4
    and 4". The former means 1/4 -- a quarter second. The latter means four
    seconds: this is sixteen times the exposure (a four-stop difference!).

    Halving or doubling the shutter speed is a one-stop difference in your
    exposure. A shutter speed of 1/4 second is one stop more exposure than
    a shutter speed of 1/8 second. This works exactly in parallel with the
    changes to aperture. An aperture of f/2.8 is one stop more exposure
    than an aperture of f/4. (a little confusing here; if you double or
    halve the f-stop number, you're changing the exposure by TWO stops: f/8
    is two stops less exposure than f/4).

    So, if your exposure was 1/4 second at f/2.8 (which in my Canon
    camera), you could get exactly the same exposure (the same brightness)
    by using 0.5 second at f/4.0. This works because you're increasing the
    shutter speed by one stop, and closing the aperture by one stop. The
    resulting exposure is exactly the same.

    Hope this helps!

    - Darryl
    madhobbit.geo, Sep 13, 2006
  7. mutefan

    AustinMN Guest

    Shawn Hirn wrote:
    Backwards. The larger the apature, the more shallow the depth of

    Larger apatures=smaller numbers. f2.8 is a larger apature than f8.

    AustinMN, Sep 13, 2006
  8. mutefan

    Bill Funk Guest

    Any basic photography book will explain this,and you can carry it with
    Bill Funk, Sep 13, 2006
  9. mutefan

    jeremy Guest

    A couple of possibilities come to mind. First you say it is a new camera.
    You may have not set things up correctly. Shots taken on new cameras have a
    tendency to be off, due to the unfamiliarity factor.

    Second, you may have had camera shake from handholding in dim light. Check
    the EXIF data to see what speed your camera used.

    Third, you mentioned autofocus. Autofocus can be easily fooled on landscape
    shots, where the mechanism cannot lock focus on the sky. Happens to me all
    the time, even in daylight. I usually set my digicam for manual focus, set
    at infinity, for landscapes.

    Fourth, autofocus may not work well in dim light. Does your camera have an
    indicator light near the viewfinder that confirms that it has locked focus?
    Many autofocus cameras determine the focus by seeking the highest amount of
    contrast across the focal range, and stopping right there. Dim light makes
    it difficult or impossible for the camera to determine at what focus point
    the highest contrast occurs. I can always tell when that happens, because
    my lock focus light blinks, rather than stays on continuously. And, if your
    camera is new, you may not have noticed how your camera tells you that it
    has locked focus.

    Suggestion: Try taking shots in broad daylight, using a tripod, and see how
    they come out. By taking the factor of the dim light out of the equation,
    you will more easily determine how your camera operates in large-aperture
    jeremy, Sep 13, 2006
  10. mutefan

    jeremy Guest

    He probably meant the smaller the aperture NUMBER is (which equates to the
    larger the aperture opening is), the shallower the DOF.

    Also, shots taken at maximum aperture will be appreciably softer than those
    taken at the lens' sweet spot--usually f/5.6--f/8.

    The price for very shallow DOF if often less overall resolution. f/2.8 may
    yield acceptably shallow DOF while maintaining respectable resolution.
    jeremy, Sep 13, 2006
  11. mutefan

    mutefan Guest


    One of the most comprehensive (and kind!) responses to a question I
    have ever posted in twelve years on Usenet. I'll write more as autumn
    progresses and I continue to experiment with your instructions/advice,
    but for now, I have used the tripod exclusively, and continued in
    Shutter Priority, and the pictures have come out not only great but
    very arty. (Today it was a fern, not a branch, that was in very sharp
    "near-focus," not a black branch.)

    Also, your suggestion to set the remote at high exposure speeds and
    high shutter speeds did not fall on deaf ears.

    Can't thank you enough.
    mutefan, Sep 13, 2006
  12. mutefan

    AustinMN Guest

    Regardless of what he meant, that's not what he typed. Whether a typo
    or ignorance, I corrected the error. Also, it's an f-stop, not an
    apature number (a mistake we both made).

    AustinMN, Sep 13, 2006
  13. Well, it wasn't the autofocus that did that. Autofocus is concerned only
    with getting the focus correct, not the exposure. If there isn't enough
    light, your camera automatically fires the flash in an *attempt* to make the
    exposure correct. However, most digital cameras of all types have the option
    of disabling the flash. Whether there would then be enough light, *at dusk*,
    is another question.

    The probability is that even wide open at f/2.8 there just wasn't enough
    light to use a high enough shutter speed to prevent blur, so the camera set
    a slow shutter speed to get the best exposure -- resulting in blur from
    camera shake. In such situations you should try using a tripod or some other
    steady support for the camera, if possible.

    That means the shutter is open for 1/4 second. Far too long (too slow) to
    get sharp pictures if shooting hand-held.

    If you liked the results, fine. But shooting at shutter speeds in that slow
    range will almost always give you a certain amount of blur, if shooting

    Opening the aperture (lower f number) *and/or* leaving the shutter open
    longer (slower shutter speed) will of course let more light through the
    lens, which obviously is what you want when shooting in low light.

    Aperture control may be useful for either. *Opening* the aperture in low
    light lets more light through, making proper exposure easier at useful
    shutter speeds; *stopping down* the aperture lets less light through which
    gives greater depth of field. I am assuming that you understand the terms
    you are using.

    Shutter speeds are exposure times given in fractions of a second. It's as
    simple as that. The usual thing when shooting hand-held is to use a shutter
    speed of about 1/50 second or faster (shorter exposure) when using a
    "normal" lens, faster than that when shooting with a long ("tele") lens or
    zoom lens set to some focal length longer than "normal," the longer the lens
    the faster the shutter speed, since longer focal lengths magnify camera
    shake in proportion. Contrariwise, wide-angle lenses (or zooms set to a wide
    angle) may be used at somewhat slower shutter speeds and still get sharp
    images hand-held.

    Using a tripod or other firm support greatly increases the range of shutter
    speeds you can use, since such support eliminates or reduces camera shake.

    Neil Harrington, Sep 14, 2006
  14. In simplest form, exposure is a balance between the amount of available
    subject light, sensor/film sensitivity (ISO/ASA), lens aperture (f-stop),
    and shutter speed. Lower subject light requires a higher sensor/film
    sensitivity, and/or a wider aperture, and/or a slower shutter speed.
    Sensor sensitivities come in numbers like 50, 100, 200, etc., with each
    higher permitting shooting in 1/2 the light level (1/3rd in-between values
    also exist). Apertures come in whole values of f1.4, f2, f2.8, f4, f5.6, f8,
    f11, f16, f22, f32, etc., and these (with larger numbers) represent 1/2
    the light exposure as you move up in value (in-between values exist, and
    many lenses with separate aperture rings permit infinitely variable settings
    for precise exposure settings). Shutter speeds come in whole values
    (in seconds) of 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/125,
    1/250, etc. (each exposes 1/2 the value of the one before, and many
    cameras permit in-between values). The choices of what to use depend
    on conditions. Low light requires high sensor/film sensitivity (400 or so,
    risking greater noise/grain), and/or a wide aperture (f2.8 or so, risking
    little depth of field and so-so lens performance [the latter is also a
    problem at stops of f16 and smaller]), and/or a slow shutter speed
    (like 1/15, 1/30, etc., risking camera shake - most evident at a
    speed about 1/lens-focal-length=shutterspeed [like for 125mm,
    figure the shutter speed should be at or higher than 1/125mm = 1/125th
    second] or slower).

    As a result of the above, many combinations give the same exposure,
    like ISO 200, f5.6, and 1/60th second equals ISO200, f8, and 1/30th
    second, which equals ISO400, f8, and 1/60th a second (for a given
    available light level...). Either the shutter speed in Shutter priority mode
    (watching for appropriate aperture selection by the camera), or Aperture
    in aperture priority mode (watching for appropriate shutter speed
    selection by the camera), or Program mode (watching to see that
    appropriate values have been selected by the camera) can be used
    under any lighting condition - and many cameras allow you to "slide"
    the equivalent values to some more to your liking). In addition, many
    cameras permit you to bias the exposure toward darker or lighter if you
    do not like the average value of the brightness of the pictures you get
    from your camera (judged on a reasonably well calibrated monitor).
    Personally, I prefer to use "A" mode and occasionally add a bit of
    exposure composition - but others prefer other ways of working.

    And, the flash on most cameras can be turned off when not needed...
    David Ruether, Sep 14, 2006
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