Focal Length and Focal Distance are not complex things to understand, and animating them over time can add a lot of dynamism and dramatic flair to a project. So, for your viewing pleasure, I’ve included several examples using telephoto lenses, a wide-angle lenses, and zoom lenses. First, an explanation of what those things are and how we measure focal length in the real world.
Focal distance is the distance between the camera lens and the subject, and can be manipulated by the photographer – move the camera toward or away from the subject. Fairly simple and straight forward, I’d say! The focusing ring, controlled by the photographer, allows the photographer to tell the camera “Hey – this is where the subject is!” It doesn’t actually have to be where the subject is – a lot of REALLY cool photographs have the foreground in focus with the subject and background out of focus. It’s really up to the photographer and his/her artistic decision making. In videography, it’s possible to start with the focus on the foreground and shift the focus back to the subject. Again, it’s all up to the photographer/videographer. Focal distance will be important for a later topic, but I thought it worth mentioning here as well.
Focal length, however, takes a LOT more time to discuss. Focal length in the real world is the distance between the light convergence point after the light hits the lens and the sensor plate of the camera (or film plate for film cameras). Focal length also has the added benefit of widening or narrowing the field-of-view (FOV) of a camera. Thus, shorter focal length lenses have a wider FOV, and longer focal length lenses have a narrower FOV. Shorter focal length lenses also widen subject features as the camera gets closer to them. Likewise, longer focal length lenses tend to compress the subject. Finally, with film and digital cameras using real lenses, the focal length is measured in millimeters although some VERY old lenses use centimeters and inches as their units of measure. In Adobe After Effects, it is measured in pixels and the corresponding FOV angle is listed parenthetically beside it. In the presets, however, focal length is given in millimeters.
There are two main types of lens construction, and two main types of focal lengths with several subcategories beyond those. For our purposes, I will discuss a few at length and mention the others in passing. Lens construction is described as either prime or zoom. That means, respectively, that the lenses have a fixed and unchanging focal length, or that they are capable of having their focal length changed by the photographer. Changing the focal length from shorter to longer gives the impression of zooming in closer to the subject, hence the name. Since the FOV is narrowed as the focal length increases, the amount of subject background that we see is also further reduced. That has practical implications for cinematographers and as we plan our shots as motion graphics artists.
Categorizations for focal length are mainly wide-angle and telephoto. The dividing line between the two is the 50mm mark. 50mm is said to most closely mimic the proportions of human sight. Wide-angle lenses are lenses with a focal length of less than 50mm. Typically, the prime lengths are 35mm, 28mm, 24mm, and 18mm. Wide-angle zoom lenses can fill in the gaps between those measures. Telephoto lenses are lenses with a focal length of 50mm or more. Typically, the prime lengths are 50mm, 80mm, 105mm, and 135mm. Telephoto zooms can, once again, fill in the gaps between those measures. The obvious question is, if zooms can fill in the gaps, then why bother with prime lenses? The answer is that it takes more mechanical “stuff” to move the lens elements in zoom lenses, so there is less room for the optics (glass elements). That means that there’s less light entering the camera, increased exposure times, etc. Prime lenses can have larger optics because they don’t move. Thus they can provide more light to the sensor, reducing exposure times and giving photographers other options (which we’ll discuss later).
There are some extreme wide-angle lenses (called “Fish-eyes”) shorter than 18mm, that provide some very interesting looks to your photography. These are typically used for special effect, and are not widely used by the average photographer. Likewise, there are Super-Telephoto lenses beyond 135mm that are used by nature photographers and sports photographers to get close to the action while standing at a distance. Again, these are not typically used by the average photographer. The Canon EF-S 500mm f/4 L IS USM II lens retails for over $10,000 – far beyond even a prosumer’s budget!
Watch this from 0:54 onward for a very cool demo of one of the world’s longest telephoto lenses.
So how does this apply to us in Adobe After Effects? Certainly, we are not limited by real-world concerns like light sensitivity, optics, mechanics, etc. But understanding the real-world roots of our settings can lead us to make more intelligent decisions in our motion-graphics work. If our aim is to make our compositing, our motion graphics, our kinematic typography, etc., fit into real-world footage, then knowing the real-world counterparts to our digital tools is essential.
After Effects allows us to control both focal length and focal distance as separate properties of the camera – either in the camera settings dialogue box or in the timeline panel. When we create a new camera by using Handmash (Andrew Devis’ clever nick name for Shift+Option+Command) + C, or by using Layer>New>Camera…, we see the following…
There are several presets for each camera; the default is 35mm. By clicking on the preset pull-down menu, we see the following…
We can also set up our own camera with our own settings by clicking on the “custom” option, or by selecting a preset and then fiddling with the settings. Likewise, we can also change the unit of measure from millimeters to either pixels or inches down in the bottom left of the dialogue box. Since I got into the visual arts through photography, I prefer to work with millimeters, but if you prefer to work with pixels or inches, please be my guest. Use whatever allows you to create great work the easiest!
Lastly, if you want to change or animate any of those settings after creating the camera, you can do so in the Timeline panel:
Focal length is now called “Zoom” here, and Focal Distance label is unchanged. Notice also that the FOV is also included in the Zoom property.
Here are a few examples of the same shot with different focal lengths, including two zooms.
Default 35mm camera – 1777.8px prime lens
500 pixel prime lens
Camera Zooms from 500 pixels to 1777 pixels after camera movement
Camera zooms from 500 pixels to 700 pixels as camera moves