Aperture and Shutter speed are undoubtedly the two most important technical aspects for any photographer to understand and master. Anyone who fully understands that these two aspects are not mutually exclusive and are in fact closely linked to on another opens up new and exciting ways to photograph their subjects. Lets review these two aspects from a technical and practical point of view.
Technical: Aperture refers to the whole within a lens, through which light travels into the camera body. The larger the hole, the more light passes to the camera sensor. In photography, aperture is typically expressed in “f” numbers (also known as “focal ratio”, since the f-number is the ratio of the diameter of the lens aperture to the length of the lens).
Practical: Aperture controls the depth of field, which is the portion of a scene that appears to be sharp, in an image. If the aperture is very small (Large F stop eg 16 or 22) the depth of field is large, while if the aperture is large (Small F stop of 2.8 or 5.6), the depth of field is small.
Technical: Shutter Speed refers to the length of time a camera shutter is open to expose light into the camera sensor. Shutter speeds are typically measured in fractions of a second, when they are under a second.
Practical: Slow shutter speeds allow more light into the camera sensor and are used for low-light, night photography, or to blur movement, while fast shutter speeds help to freeze motion.
F20 @ 1/10s
Understanding the Relationship between Aperture and Shutter Speed
Lets assume that you are shooting in Aperture Priority mode – one of the most frequently used modes for wildlife photography. If we understand the technical and practical applications of aperture and shutter speed, we can use this understanding to control far more than just depth of field in this mode.
Based on the above you should be able to see that we are able to control the amount of light entering through the lens and falling onto the camera sensor by adjusting the aperture. By selecting a larger aperture (eg f2.8) we allow more light to enter which results in the camera using a faster shutter speed to capture a correctly exposed image.
On the flip side, if we dial in a small aperture (eg. f 16) we reduce the amount of light that enters through the lens, resulting in the camera using a slower shutter speed in order to obtain a correctly exposed image.
The Practical Application
So we know now that we can manipulate our shutter speed with our aperture settings when shooting in Aperture Priority Mode. This not only opens up a wide variety of ways of using shutter speed in a creative manner (check out this blog post for a couple of neat examples on this) but it allows us to switch between freezing movement and blurring movement in a very short space of time, without needing to change camera modes. Understanding this relationship between aperture and shutter speed allows you explore various creative means of photographing a single subject in a very short space of time.
The “Trump Card” : ISO
I have touched on two of the three points of the well known exposure triangle. The third of these elements is ISO and this really is somewhat of a trump card.
Technical: ISO effectively increases the sensitivity of your camera’s sensor to available light. A lower number represens lower sensitivity to available light, while higher numbers mean more sensitivity. More sensitivity comes at the cost though, as the ISO increases, so does the grain and digital noise in your images.
Practical: Increasing your ISO will increase your shutter assuming that you do not alter your chosen aperture. This is great for ensuring that you eliminate any chance of camera shake creeping into your images (check out this post for 10 tips on improving your photography). On the flip side, if you are wanting to make use of slow shutter speeds, you can drop your ISO as low as possible to drop your shutter speed to an appropriate speed for capturing the motion that you are focussing on.
So there you have it. Aperture and Shutter Speed are intimately linked and if you can grasp this fact you will be able to manipulate both variables in Aperture Priority mode alone, saving you precious time and allowing you to explore more creative ways of photographing your subject.
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