The essence of any photographer, apart from building creative vision, is to control exposure. The ability to control motion using shutter speeds and controlling depth of field using aperture is a sure way of achieving this. As a prologue, let’s recap how a DSLR (Digital Single Lens Reflex) camera works.
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Light enters the Lens, hits the mirror, is reflected to the pentaprism to the viewfinder. The mirror moves up to allow light to get to the sensor. The shutter also gets out of the way to allow light. The figure above illustrates this.
The camera shutter controls the duration that light is entering the camera and exposing the sensor. The duration with which the shutter remains open will determine the intensity of light coming through. The longer the time the shutter remains open, the more the light. Conversely, the shorter the time the shutter remains open the less the light. Shutter speeds are usually measured in seconds or fractions of a second.
1/4 – 1/8 – 1/15 – 1/30 . . . . . . . . . . . 1/200 – 1/400 – 1/800
<— Slower shutter speeds Faster shutter speeds –>
Some cameras show shutter speeds using whole numbers;
2 – 5 – 8 – 15 . . . . . . . . . . . . . . . . 30 – 60 – 125
When using whole numbers, fractions of seconds is denoted using inverted commas as shown below
1″ – 2″ – 4″ – 8″ . . . . . . . . . . . . . . . 15″ – 30″ – 60″
Any shutter speeds above 30 seconds is called the Bulb Mode.
When you change shutter speed, you control duration of light into the camera. This affects or controls how motion is captured. This will result in either blurred or frozen image. The image below shows the difference between the two;
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Another showcase of slow shutter speed can be seen in a photo taken at night on a busy highway. The typical shutter speed to blur the headlight and tail light of cars is about 60 seconds.
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The intensity of blur depends on how long the shutter is open. This is exhibited no better than the image below which shows the blur of the sky from the ground that picks up from the earth’s rotation. In this case, the shutter is open for 1 hour.
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As a precaution, it is recommended that you should avoid camera shake especially when the shutter is open for a long duration. Any form of shake will result in blurred image across the entire image. It is therefore advisable to mount a camera to a tripod despite the fact that some lenses come with in-built IS or VR (Image Stabilization and Vibration Reduction respectively). Using slow shutter speed during the day necessitates the use of filters. Typically, shutter is usually denoted as ‘S’ (Shutter) or ‘Tv’ (Time Value) on the main dial of the camera.
Aperture controls the amount (how much) light enters the camera. Aperture blades control how much light is taken through. Aperture is expressed as F numbers or F stops. The larger the number the smaller the aperture size.
F/1 – F/4 – F/5.6 – F/8 . . . . . . . . . . . . . . . . . . . F/18 – F/22 – F/30
Big aperture (Shallow depth of field) Small aperture (Deep/wide depth of field)
Aperture affects visual of images, also referred to as depth of field. This is to determine how much of the scene is on focus. You may want to emphasize the subject by blurring the background. Shallow depth of field results in small area in focus and thus an image with blurred background. A deep/wide depth of field results in a large area of focus in image. Depth of field focuses on the subject under focus. Kindly note that refocus does not change the depth of field. The below image shows the difference between shallow and deep depth of field.
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