Camera Exposure Basics: Shutter Speeds, Aperture, F Stops, and ISO

    In photography, the term exposure is a reference to how much light, and how long that light is exposed to the
    cameras' image sensor when the camera shutter release is pressed.

    In simple terms, the camera's exposure value settings determine if an image will be too light, too dark, or correctly
    exposed according to normal standards.

    The correct or desired exposure is obtained by using a combination of the camera's  Lens Aperture setting, the
    Shutter Speed, and the ISO setting. Those three functions are commonly known as the "Exposure Triangle".

    All digital cameras have automatic shooting modes which enable you to just pick up your camera and start taking
    pictures without having to worry about the settings for a correct exposure. That would include basic compact cameras
    like the Canon  Powershot Elph 135.

    Still, it is good know what the camera is doing to obtain the exposure even with a basic compact camera. That is just
    in case you need to change from the full automatic mode to a scene mode like night landscape or back lit portrait to
    adjust for various light conditions.

    However, Digital SLR cameras like the Canon T5i, or Mirrorless Compact System cameras like the Sony NEX5T allow
    you to manually adjust all of the camera's exposure settings. Some "Bridge"  type cameras also allow you to manually
    choose specific settings to adjust the exposure.

    With most basic compact cameras, the exposure settings are automatically set and cannot be manually adjusted.

    What are the functions of the Aperture, Shutter, and ISO rating?

    As previously mentioned, the camera lens aperture, the camera shutter, and the ISO function work together to
    produce a correctly exposed image. Lets take a look at each of these functions individually, and then how they work
    in relation to each other.

    The Lens Aperture: The camera lens aperture, or more specifically, the
    size of the lens aperture opening determines the amount of light that reaches
    the camera's image sensor. The camera lens aperture diagram on the right
    shows the relative size of the aperture openings at different settings.

    The various lens aperture settings are called "F Stops". The aperture settings
    with the lower F Stop numbers allow more light to reach the image sensor
    than the settings with the higher F Stop numbers.

    Listed below is an aperture chart. The F Stop numbers in red represent a full
    stop and the numbers in black are 1/3 increments between the full stops.

    A full stop in either direction will allow twice as much light, or half as much light
    to reach the image sensor. For example, F4 allows twice as much light to reach
    the cameras' image sensor than  F5.6. On the other hand, F8 allows half as
    much light to reach the sensor than F5.6.

    Take a look at picture # 1. It was taken with the lens aperture set to F10 and is much darker  than picture # 2, which
    was taken with an F5 aperture setting. That is because the wider aperture opening of F5 allows more light to reach
    the image sensor than the smaller aperture opening of F10. In this example, the shutter speed and ISO settings are
    the same in both pictures.

    You can see that even though the only setting that was changed was the lens aperture, the images look totally  

    Another important feature of the camera lens aperture is its effect on the Depth of Field in an image. Depth of field is
    a reference to how much of the image, (subject, foreground, and background) will be in focus. Using a wide aperture
    such as F2.8 or F3.5 can produce an image similar to
    picture # 3. Notice how the flower is in focus but the
    background area is out of focus. That effect is referred
    to as narrow, or shallow depth of field.

    Using  a smaller aperture opening like F11 or F16 might
    produce an image like picture # 4 where just about
    everything is pretty much in focus. That effect is called
    wide depth of field.

    However, take note that there are other factors such as
    the lens focal length,the lens to subject distance, and
    the type of camera lens being used that will also affect
    the depth of field in an image.

    The Camera Shutter: The shutter speed determines the length of time that light will be exposed to the camera's
    image sensor. Shutter speeds are listed in seconds or fractions of a second. Those times reflect how long the camera
    shutter will be open during an exposure. Listed below is a chart showing shutter speeds in full steps and in 1/3 step
    increments. The numbers in red represent a full step or stop.

    A shutter speed of 1/60th of a second keeps the shutter open longer than a shutter speed of 1/125th of a second.
    Changing the shutter speed by a full or partial step in either direction is the equivalent of changing the lens aperture
    setting by a full or partial F Stop in the same direction.

    Lets refer back to picture # 1 in the lens aperture section. It is clearly too dark. The underexposure was corrected
    by changing the aperture setting from F10 to F5 which allowed more light to reach the image sensor. However, If
    you wanted to lighten that same picture without changing the aperture setting, you could simply change your shutter
    speed instead.

    Changing the shutter speed from 1/400 to 1/100 will allow the light to be absorbed by the image sensor for a longer
    period of time. That change will yield the same basic result as changing the aperture from F10 to F5. The point here
    is that changing the shutter speed by any given amount of  "steps" or increments will have the same effect as
    changing the aperture by an equal number of steps. (as long as the change is in the same direction)

    The shutter speed also has an effect on the look of an image when there is motion in a scene. If there is fast
    movement  in a scene, you might need to use a fast shutter speed to avoid motion blur. Take a look at the moving car
    in picture # 5. The car in the picture is blurred because the shutter speed of 1/60 was not fast enough to "freeze" the
    subject. The car in picture # 6 was shot using the faster shutter speed of 1/250 which was fast enough to "freeze" the
    movement of the car.

    On the other hand, there may be times when using a slower shutter speed might be your best or only option. For
    instance, if you try to take pictures at night using a shutter speed like 1/250,they will almost certainly come out black or
    severely underexposed. Sometimes that will happen even if you use your widest lens aperture opening.

    Picture #7 was taken in a fairly well lit area by night photography standards.
    The shutter speed was 1 full second with a somewhat wide aperture setting
    of F 3.4. Can you imagine what the image would look like if it had been taken
    using a shutter speed of 1/250? (assuming the same lens aperture and ISO
    settings were used)

    The ISO Function: The ISO setting determines the image sensors' sensitivity
    to the available light. Lower ISO number settings will require more light  for
    the image sensor to produce a good image than when the camera is set to
    a higher ISO number. A camera set to ISO 400 will need less light to produce
    a correctly exposed image than when it is set to ISO 100.

    The following are a few of the most common ISO settings. (there may be more
    that show in your camera but we will just use these to keep things simple)

    It is usually best to use lower number ISO settings when taking pictures. That is because the overall quality of the
    image will be better. Higher ISO number settings tend to produce grainy images that have tiny specks called digital
    camera "noise". (Check the tutorial "What is ISO" for an example)

    However, there may be times that using a higher ISO setting might be the best way to go. A simple example might be
    when you are in a poorly lit place and your pictures are coming out too dark. If your camera is set on ISO 100, change
    it to ISO 200, ISO 400 or whatever setting gives you a lighter picture.( that is, in situations where the shutter speed
    and aperture settings are not the primary concern) Remember, the higher number ISO settings require less light to
    produce a well exposed picture.

    Here is another example of when you might need to change the ISO setting. Lets say you are at an indoor sporting
    event with lots of fast movement. Your camera is set to ISO 100. The cameras' exposure metering system suggests
    a lens aperture setting of F4 and a shutter speed of 1/30 for a correctly exposed picture. (assume that F4 is your
    maximum aperture width)

    You know that a shutter speed of 1/30 won't be fast enough to "freeze" the action. However, a shutter speed of
    1/250 should work well. Change your ISO setting from ISO 100 to ISO 800. Next, change your shutter speed from
    1/30 to 1/250. You will probably be able to take a properly exposed picture with the action "frozen" instead of blurred.

    As you have probably noticed, changing the ISO setting by a certain number of steps is the same as changing the
    shutter speed the same amount of steps. That principle also applies to the ISO in relation to the aperture setting.

    Aperture Priority, Shutter Priority, and Program modes: The majority of material in this tutorial refers to using
    your camera in the Manual mode where you can set the lens aperture, shutter speed, and ISO separately.  

    Just remember that you don't always have to set each function individually each time you take a picture. Try using
    one of your cameras' semi automatic modes. If the shutter speed is most important to you for a particular shot, try
    using the Shutter Speed Priority mode. When using the Shutter Speed Priority mode, you set the desired shutter
    and the camera will automatically set the aperture that should produce a correctly exposed image.

    On the other hand, if the lens aperture setting is most important to you, try using the Aperture Priority mode. You
    choose the lens aperture setting you want to use and the camera will set a shutter speed that should produce a
    correctly exposed picture.

    Lastly, if you aren't concerned about shutter speeds or aperture settings but want to change your ISO at times. Just
    use your camera's program mode. In the program mode the camera will automatically choose the shutter speed and
    aperture setting for the best exposure. In the Program Mode you will still be able to change the settings for things like
    the ISO and White Balance.

    If you are in the market for a good Digital SLR camera, check the Nikon D5300. Looking for something else? Just
    click on any of the camera advertisements on this site. There are plenty of cameras to choose from and the dealers
    are all reputable.
Overexposed Image
Underexposed Image
Better or "Correct" exposure
camera lens aperture f stops
Camera Exposure Basics picture#01, aperture F10, shutter speed 1/400
Camera Exposure Basics picture #02, aperture F5, Shutter speed 1/400
Picture #2   Aperture F5,
Shutter Speed 1/400, ISO 64
Picture #1   Aperture F10,
Shutter Speed 1/400, ISO 64
Wide depth of field image, Camera Exposure Basics
Picture 3, Narrow Depth of Field
Shallow depth of field image, camera exposure basics picture #03
Aperture Chart with Full and 1/3 F Stop Settings
Camera Lens Aperture Diagram
Shutter Speeds listed as Full and 1/3 Steps
camera exposure basics, shutter speed, blurred movement
Camera exposure basic, shutter speed, frozen motion
Picture 4, Wide Depth of Field
Picture #5, Shutter Speed 1/60
Picture #6, Shutter Speed 1/250
ISO Settings
Camera exposure, slow shutter speed picture
Picture #7, Shutter Speed 1 second,
Aperture, F 3.4,  ISO 400
Correctly exposed picture
Underexposed picture
Overexposed picture
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