The aperture in a camera lens can be likened to the iris in the eyes. Under dim light, the irises in our eyes enlarge to accommodate more light. They also contract to limit the amount of light entering the eyes under bright light. The f/stop or aperture in a lens performs a similar function as the iris. The aperture does more than just control exposure; it can be used to enhance your creativity. It helps to provide sharper images and to take out a background from the point of focus.
Aperture and the amount of light
An aperture is synonymous with the amount of light. It may cut the amount of light that strikes the sensor by half or double the amount. They can either add light (open up) or reduce light (close up).
Maximum f/stop and lens speed
An aperture is described as a maximum f/stop when it accommodates the highest light intensity to the sensor—the lens speed increases as the maximum aperture increases. An f/2.0 lens is a stop faster than an f/2.8 maximum aperture.
The cost of a lens increases with its speed.
It is more expensive to purchase faster lenses—the faster the lens, the greater the weight. A Canon 85mm with an f/1.2 lens weighs 36.16 ounces, while an 85mm f/1.8 lens weighs 15 ounces since the f/1.2 lens is faster than the f/1.8 lens.
Uncommon types of apertures
It is rare to find very fast lenses with an aperture between f/0.5 to f/1.0. An f/0.7 aperture was used to shoot Barry Lyndon candle-lit scenes. You can find apertures above f/32 on cameras with larger formats with maximum aperture starting at f/2.8 to above f/8.0.
Depth of field (DOF)
Depth of field describes the areas of sharpness behind or in front of the acceptable focal point. The DOF extends about two-thirds of the area behind the focal point and one-third of the area in front of the focal point. The aperture and focal length are two primary factors that determine the apparent DOF.
Although most lenses have similar DOF, deviation from focus is less common with wide angles than with telephones. According to the rule of thumb, lenses with wide angles have a higher DOF than lenses with longer focal lengths.
A lens’s maximum aperture has a lesser DOF than its minimum aperture. The picture below of a flower taken with an f/1.8 50mm lens. At this maximum aperture, the results show a sharp focal point with a compelling subject that draws your eyes to the primary subject.
Photo by Etienne
The minimum aperture would produce the opposite effect where the whole frame would be in focus not just where focal length allows because of aperture. The image below highlights the minimum aperture in making a sharp image from the foreground to the background.
Photo by Jim Choate
Bokeh is a Japanese word that describes blur or those highlights that are out of focus. The aperture settings control the bokeh size. The bokeh gets bigger as the lens is set closer to the maximum aperture. Reducing the lens reduces the bokeh size. The more highlights that are out of focus, the more rounder they will appear.
The number of blades making up the lens’ aperture determines the roundness or shape of a bokeh. The higher the number of blades in an aperture, the rounder the shape of the bokeh. You can count the number of sides of the bokeh to determine the number of blades present in your lens’ aperture.
Andrew Farron works for Fable Studios, a Creative-led boutique video and animation studio that creates tailored brand stories that endure in your audience’s mind. Fable combines your objectives with audience insights and inspired ideas to create unforgettable productions that tell the unique story of your brand.