Aperture (or the long overdue blurry background post)

Understanding the concepts behind your camera’s aperture settings will likely bring a tremendous level of creative control to your photography.

Simply stated, the Aperture of a lens is the size of the opening though which light can enter the camera.  The larger the opening, the more light.  To use a cooking analogy, if Shutter Speed is how long you cook it, then Aperture is the temperature of the oven.  They need to balance each other out to achieve proper results.

To get the technical stuff out of the way, similar to shutter speeds, aperture settings are measured in stops.  Specifically known as f-stops, the larger the opening, the smaller the number.  It’s confusing, but once it clicks for you it will become second nature.  On most lenses, the smallest opening is f/22, while the largest opening varies greatly.  Generally speaking, the larger a lens can open up, the more expensive it is.  Pro lenses are typically f2.8 or below, while most kit lenses are in the f3.5 – f5.6 range.  Check your lens to see what the maximum aperture is.

While the core purpose of adjusting f-stops is to achieve a proper exposure, there are side effects (both desirable and undesirable) that allow you to exert more creative control.  Specifically, the aperture setting will affect how much of the photograph is in focus.  This is known as the “Depth of Field”.   Smaller openings (f/16 or f22 for example) allow for objects near and far to be in focus, while larger openings ( f/2.8) will limit how much of the photograph is in focus.

Example of shallow Depth of Field achieved using a low aperture (f1.8)

Many times, it’s desirable to have this “shallow” depth of field.  It will isolate the subject and effectively leave the background blurry.  Frequently used for portraits and wildlife photography, it helps to direct the viewer’s eye to the intended subject of a photograph.

Other times, it’s desirable to have much more of a picture in focus.  Landscapes come to mind as a typical example.  To achieve sharp details across a long distance, small f/stops are necessary.

Example of a large Depth of Field achieved using a high aperture (f16)

SO HOW DO YOU CONTROL IT?  First, move your camera into “Aperture Priority” mode, typically done by moving the mode knob to A or AV.  Now you can select an f-stop, and the camera will figure everything else out.  Next find the aperture control.  On old cameras  it was actually on the lens, but today it’s often a dial near your thumb or forefinger.

WHEN WOULD YOU USE IT?  Any time you want to isolate a subject.  Alternatively any time you want the background to be in focus.

WHATS THE DOWNSIDE?  When shooting at low apertures (wide openings), it’s easy to “miss” your focus.  This will result in having the wrong part of a photograph in focus.  As discussed in the post on Controlling  your Focus, it’s important to know how to place a focus point on the intended subject.  Mistakes are exaggerated with lower apertures. With extremely low apertures, depth of field can be limited to a few centimeters.  In the example below, Harley’s eyes are in focus, but his nose and ears are not.  In fact, I probably missed it here as the hair on his nose is sharper than his pupils.  However had I focused on the ears by accident, his whole face would be blurry.

Extremely shallow Depth of Field at f1.8

Inversly, shooting at high apertures will require longer shutter speeds.  This can create problems resulting from a moving subject or more commonly, camera shake.  This is why most landscape photographers use a tripod – keeps the camera steady and allows them to use smaller apertures to achieve sharpness across a distance.

I encourage you to put your camera in A mode and just start shooting.  Shoot the same piece of fruit at each f-stop and you’ll see the background go in and out of focus as you scroll through the pictures.  You’ll be amazed at how much your portraits improve when shooting at lower apertures.

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