Need to Know: Understanding Focal Length & Aperture

What is Focal Length?

To clarify, a len’s focal length is not a measure of its physical dimensions; rather, it is a description of its length & range measured in millimeters (mm). Focal length encompasses various optical elements that aid in focusing light & reducing distortions. The point where all light rays converge to create a clear image is referred to as the optical center of the lens. A longer focal length suggests that light bends gradually, whereas a shorter focal length suggests sharper angles of light bending. Typically, lenses with positive focal length converges light, while those with negative focal lengths diverge light, though there are expectations depending on the distance between the lens and the object being photographed.

Knowing the Right Language

Before we go any further, it is important to know the practical effects that focal length has on image-making. There are four key areas you should know:

Field of View

The field of view refers to the visible area captured by a lens system, essentially what fills the camera’s sensor. It can be quantified by the physical area that can be imaged, whether in horizontal or vertical measurements (in mm), or in angular measurements (in degrees).

Subject Size

In photography, the focal length of a lens determines how subjects appear in your images relative to the distance between you and them. With shorter focal length lenses, subjects and objects will appear smaller, while longer focal lengths will make them appear larger, creating different perspectives and visual effects in your photos.

Perspective

Perspective relates to the optical illusion where in closer objects seem larger, while those farther away appear smaller. By carefully selecting the point of view, filmmakers guide audiences through a narrative, subtly influencing their emotional journey. This decision impacts how viewers connect with characters, settings, and the underlying themes of the film.

For instance, a first-person perspective can immerse viewers directly into the character’s emotional state, creating an intimate connection. Alternatively, an omniscient camera angle might provide a god-like overview of the story, offering audiences insight into multiple characters and plot developments simultaneously.

Image Shake

Image shake refers to the blurriness and loss of image quality caused by the vibrations when pressing the shutter release. When shooting with a lens featuring a longer focal length and a narrow perspective, even the slightest movement can be amplified, leading to image shake. To mitigate this, using a tripod can provide stability and help ensure sharp, clear images.

Image credit: NixonUSA

Focal length isn’t just about capturing an image—it’s about shaping the narrative. Picture this: a wide-angle lens pulls the viewer into the heart of the action, immersing them into the scene. It’s like they’re right there, part of the story unfolding before their eyes. On the flip side, a longer focal length zooms in, focusing the viewer’s attention on specific details, heightening tension, or conveying intimacy between characters. Each focal length choice is like a brushstroke on the canvas of your story, influencing the mood, perspective, & emotional impact. So, whether you’re capturing sweeping landscapes or intimate character moments, the focal length is your storyteller’s tool, guiding your audience through the narrative journey with every frame.

What is Aperture?

Aperture isn't just about controlling the amount of light entering the lens—it's a powerful tool for shaping the mood and atmosphere of your visuals. Aperture pertains to the opening through which light travels before reaching your camera sensor.

Here is a concise graph detailing the effects of aperture. Image credit: CaptureLandscapes

As you can see in the chart above, the aperture affects more than just lighting, but also the depth of field & sharpness. To avoid confusion, depth of field is NOT the same as field of view. DOF refers to the area of sharpness behind and in front of the subject. Depending on the f-stop (aperture’s numerical value & lens specification), you can determine how large or small you want your aperture for the shot. By regulating the size of this opening, we can manage the amount of light captured in an image & also determine the depth of field. When you widen the aperture to let more light in, you're not just brightening the scene; you're also narrowing the depth of field. This creates a beautifully blurred background, drawing the viewer's attention to the main subject while gently softening the surroundings. It's like isolating your subject in a dreamy bubble, enhancing their importance and creating a sense of intimacy.

On the other hand, when you stop down the aperture, you increase the depth of field, bringing more of the scene into sharp focus. This can be perfect for widespread landscapes or shots where you want every detail crystal clear. It's like opening up the world for your audience to explore, inviting them to immerse themselves in the richness of the environment. However, aperture isn’t solely about technical adjustments—it’s a key element of storytelling! A wide aperture can evoke a sense of intimacy, romance, or mystery, while a narrow aperture can convey grandeur, expansiveness, or a meticulous attention to detail. By mastering aperture and depth of field, you're not just controlling the technical aspects of your shot; you're sculpting the emotional landscape of your visual narrative, guiding your audience on a journey through light, shadow, and storytelling magic.

Congratulations! Having grasped the concepts of focal length and aperture, you've taken a crucial step toward mastering your camera. Now, it's time to pivot into the next phase. Join me as we explore the various types of lenses that an aspiring filmmaker, like yourself, will consider for your upcoming projects!