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Exposure: Shutter Speed, Aperture, ISO
Posted By: ltdstar, 06-05-2009, 06:27 PM

There are three parameters that you can adjust to change your exposure. These are: shutter speed, aperture, and ISO. All D-SLR have buttons, dials, or from a menu to make adjustment to each. Refer to your camera for reference. This will give you an idea of how these are interconnected and you can explore your way out of the auto mode on your camera.

Shutter speed: the duration in which the shutter remain open once the shutter button is released. The faster the shutter speed, the less amount of light able to reach the sensor effectively decrease the exposure (dark). The longer the shutter speed more light will reach the sensor therefore the image will be brighter. There are tradeoff for using slower or faster shutter speed depending on the condition of your location. Faster shutter speed enable you to freeze motion but you will need sufficient light to exposed correctly. It will also eliminate any motion blur from your shaking hand or motion induced from the release of the shutter button. The benefit of using slower shutter speed is to gain exposure in less than ideal lighting condition. Longer shutter speed will make the flow of water from a stream or waterfall more milky. However, motion blur will be a problem with slower shutter speed so tripod is a must for long shutter speed. Slower shutter speed are only used on static object/scenes.

Faster shutter speed:
  • +freeze motion
    +eliminate motion blur
    -require lots of light

Slower shutter speed:
  • +gain exposure
    +milky moving fluid effect
    -motion blur
    -require the use tripod
    -only used on static object/scenes

Aperture: the diameter of the opening of the diaphragm in the lens. Aperture are measure by f-stop number, the larger the aperture the smaller the f-stop number. The larger the aperture the more light is allow to reach the image sensor in a given time therefore gain in exposure. However, with larger aperture, the depth of field (DOF) is decrease. DOF is the area in which it is in focus in an image. There are times when low DOF (larger aperture) is prefer, such as in portrait photography where you want to background to be out of focus and just have your subject in focus. This will isolate your subject from the background and remove any distraction coming from the background. The out of focus area is refer to bokeh and I will discuss it in later post. On the other hand, the smaller the aperture, the less light is able to reach the sensor therefore the image will render underexposed. The other effect from smaller aperture (larger f-stop) is the increase in DOF. The lens will generally be sharper once stopped down to a smaller aperture (~f8) than compare to wide open.

Larger aperture:
  • +gain exposure
    +/-less in focus area (low DOF)

Smaller aperture:
  • +sharper stopped down
    +more DOF
    -require sufficient light

ISO (film speed): the measure of image sensor sensitivity to light. The higher the ISO, the more sensitive it is to light as well as producing more noise. The lower the ISO the less sensitive the image sensor is and producing less noise. Some camera can handle noise much better than other, but hopefully between adjusting the shutter speed and aperture will give you room to use an ISO that give you noise at an acceptable level.

Last edited by ltdstar; 02-19-2011 at 01:37 PM.
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