To put it simply, aperture is an opening within a lens, which regulates how much light enters the camera. But, when dealing with aperture you have to think in opposites. Bigger is smaller. Smaller is bigger. More is less. Less is more. Aperture is measured in what are called f-stops or fractional stops, which is the ratio of the diameter of the aperture opening to the length of the focal lens. For example, if I have a 50mm lens and my aperture opening has a diameter of 25mm, then my f-stop would be 2 or f/2.0. The smaller the f-stop the larger the opening, hence all that backwards talk. The diagram below shows aperture openings at different f-stops. Along this scale the amount of light that enters the camera is either doubled or halved, depending on whether you are decreasing or increasing your f-stop number.
Lenses with large apertures(f/1.2) are considered “fast lenses” since they can capture images more quickly in low light situations. You won’t find many lenses on the market that have a larger aperture than f/1.2, although they are out there. The Zeiss Company manufactured a lens for NASA in the 60s that has a maximum aperture of f/0.7, so they could capture images on the dark side of the moon. Legendary filmmaker Stanley Kubrick managed to secure one of these lenses and used it to film Barry Lyndon. The extraordinary aperture on this lens allowed Kubrick to film using only natural light and candlelight, a feat unheard of in modern filmmaking.
Besides regulating the light that enters the camera, aperture also determines how much depth of field you have in your photos. A smaller aperture will result in a larger depth of field, with the foreground and background of your scene in focus. On the other hand, a larger aperture will result in a shallow depth of field with a small plane of focus. The photo below is an example of a shallow depth of field using a large aperture.
To make it even “clearer”, I have compiled the sequence of shots below using three different aperture settings. The first shot was taken with the largest aperture possible on my 50mm lens, f/1.8. Notice how the background is roughly blurred and even the base of the chair around the cat, as all of our focus is on the ceramic feline. Shot two was taken at an aperture of f/5.6 and you can start to see the wooden pegs and records come into focus. Finally, shot three was taken at an aperture of 18, which brought the wooden pegs into full focus and gave more clarity to the vinyl collection in the background. It should be noted that as I increased my aperture value, my shutter speed decreased in order to capture the same amount of light. Stay Tuned for Part 2 of The Three Pillars of Light, regarding Shutter Speed.
Understanding aperture is a key component into capturing some creative and unique shots with your camera. We are excited to see what great shots you will take with this newfound knowledge!