Aperture controls the depth of field and is arguably the most important element of the exposure triangle (ISO, shutter speed, and aperture). Aperture is one of the three elements that contribute to exposure and will influence the settings needed for ISO and shutter speed.

Exposure Triangle Image

What is aperture?

Aperture is the size of the opening in the lens controlling the amount of light reaching the sensor. A large aperture has a wider opening and allows more light to reach the sensor, while a small aperture is more narrow and allows less light to reach the sensor.

Aperture Graphic

Think of aperture as the pupil of your eye. Do you ever turn the light on first thing in the morning and it’s painfully bright for a second? In that split second it takes to adjust, your pupils are changing from a large diameter to a small diameter to let in less light. The opposite is true when you turn off the lights at night and it takes a second before you can see where you are going. When you turned off the lights, it takes a second before you can see while your pupil widens to let in more light.

Simply Put:

  • Large aperture = more light
    • If using manual mode, you’ll want to use a faster shutter speed and/or a smaller ISO.

  • Low aperture = less light
    • If using manual mode, you’ll want to use a slower shutter speed and/or a higher ISO.

How Do I Use Aperture?

Rain Drops on a Sprenger's Tulip

A large aperture (small f-stop number) isolates your subject by blurring the background and/or foreground. A large aperture is ideal for macro photography, portraits, blurring out distracting backgrounds, and low-light situations. Back to the pupil analogy; have you ever gotten your eyes dilated at the eye doctor and everything is blurry? That’s because they enlarged your pupil.

In this image, I used a large aperture (f/2.0) to achieve the blurred background

Arlington National Cemetery in Spring

A small aperture (large f-stop) makes the entire image sharp and is ideal for landscape, architecture, and creating sun-glare.

In this photo, I used a large aperture (f/11) so the whole scene is sharp

What is f-stop and how does it pertain to aperture?

The f-stop number is the numerical representation of aperture. The lower the f-stop number, the larger aperture. f/1.8  is a much larger aperture than an f/16. This may seem to be the opposite of what makes sense – in short, the f-stop number is actually a fraction. If you’re interested in understanding the numbers in detail, check out PhotographyLife’s blog on aperture. Otherwise, just remember that f-stop numbers are the opposite of aperture size.

Test yourself!

See if you can guess the size of the aperture used (small or large), bonus points if you can guess the actual f-stop.  Put your answers in the comments!

Answers listed under each picture.

Peregrine Falcon
Small, f/2.8
Sunset in White Sands National Park -  Las Cruces, New Mexico
Large, f/11
Autumn Leaves Falling
Small, f/3.5
Père Lachaise Cemetery in Paris, France
Large, f/11


Aperture Pin

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