Understanding F-Stops: How to Use F-Stops in Photography

An f-stop is a camera setting that specifies the aperture of the lens on a particular photograph. It is represented using f-numbers. The letter “f” stands for focal length of the lens.

A camera’s aperture is the hole in a camera’s lens that appears when the camera’s shutter opens. An aperture is circular; on a manual camera, it is produced by physical blades that form a ring around the camera lens.

• A large aperture is a circular opening with a relatively wide diameter.
• A small aperture is a circular opening with a short diameter.
• A medium aperture falls somewhere in between the two extremes.

Learn more about aperture in our guide here.

Different lenses are capable of producing different sized apertures. Lenses impact both the size of the aperture and the diameter of the aperture. The size of a particular aperture is expressed using what’s called an f-stop. You can find out how to use different camera lenses in our guide here.

The aperture scale is represented as a series of f-numbers, and those numbers can be read like fractions with “f” in the numerator. This means that:

• Smaller numbers in the denominator equal a larger aperture setting
• Larger numbers in the denominator equal a smaller aperture setting

F-stop numbers are not uniform across all photography equipment, and can depend on the type of camera you have. Most photographers who have photographed with a Nikon or Canon camera will however be familiar with some common f-stops on the aperture scale:

• f/1.4 (a very large aperture to let in as much light as possible)
• f/2.0 (lets in half as much light as f/1.4)
• f/2.8 (lets in half as much light as f/2.0)
• f/4.0
• f/5.6
• f/8.0
• f/11.0
• f/16.0
• f/22.0
• f/32.0 (the smallest standard aperture, lets in almost no light)

Remember that every f-stop number represents an aperture setting in relation to the lens’s maximum aperture. The larger the value of the f-stop number’s denominator, the less light will enter the lens.

An f-stop value will determine how much light is allowed to enter the camera lens on a given photograph.

• Employing a large aperture in full sunlight will welcome in an enormous amount of light, such that the image will be “washed out.” When using physical rolls of film, vast amounts of sunlight can literally burn the image, rendering it useless.
• On the other hand, using large apertures at night are essential to making sure a picture is adequately lit, such that its subjects can be sufficiently visible. A scene lit by a full moon (and nothing else) can be surprisingly bright if it is photographed with a wide-aperture camera exposure.

F-stops also work in concert with shutter speeds in the equation that brings light to a photograph. Shutter speeds determine how long the camera lens remains open, while f-stops determine how wide the aperture will be during that brief period that the lens is open.

• A wide aperture with a rapid shutter speed may not bring in as much light as a medium aperture with a very slow shutter speed.
• A tiny aperture with a slow shutter speed may let in more light than one realizes, and it may be appropriate for time-elapsed photography.

Professional photographers know that an f-stop is only one component that affects a camera’s output. Other factors, like the focal length of a lens and the intensity of a light source, can be equally important. In particular, photographers refer to an “exposure triangle” of factors that affect the image a camera produces. The components to an exposure triangle are:

• Aperture (denoted by f-stop number)
• Shutter speed
• ISO (which represents film sensitivity, but can be manually controlled on today’s digital cameras)

Selecting the ideal f-stop on a camera’s manual mode takes experience filled with much trial-and-error experimentation. In this way, it’s no different from every other element of photography. In truth, there’s no one correct exposure for a particular photograph in a particular light. The artistic choices of a photographer can be as important as any set edict for aperture size or aperture value. Nonetheless, as a general rule:

• Bright sunny days call out for small apertures or f-numbers with large values in the denominator.
• Dark skies or indoor photography calls for wider apertures or f-numbers with small values in the denominator
• Adding a flash makes the needed aperture smaller
• Large apertures are great for shallow-focus portrait photography where the foreground subject is very clear and the background is blurred. This is sometimes called the “bokeh” effect. Headshot photography employs this depth of field effect, and many of today’s cell phones create it in “portrait mode” by using two lenses with two different f-stops to play with the depth of field.
• By contrast, if you want a foreground subject and a background to achieve relatively equal focus, smaller apertures (which feature f-stops with larger denominators) are the way to go.

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