2.4 Lenses and Focal Length
You can't really talk about apertures, f-stops, and depth of field without understanding a little more about lenses. Camera lenses vary greatly from brand to size, but they all have f-stops and perform the same functionthey bring light into the camera. Film cameras and many new digital cameras have interchangeable lenses to change from wide-angle shots to telephoto. But in the digital world, you don't have to change lenses; instead, you change focal length and zoom factors. The focal length in most 3D applications equates to that of a real-world lens (see Figures 2.5, 2.6, 2.7, and 2.8). Although the values are not exactly accurate across the board, it's the focal length setting that will provide a wide-angle or telephoto look.
Figure 2.5 The SoftImage XSI camera panel offers specific presets for various types of lenses.
Figure 2.6 LightWave 3D 7.5's Camera panel offers a range of real-world settings to match camera lenses, as well as aperture.
Figure 2.7 Maya's Camera panel also offers control over focal length and more.
Figure 2.8 3ds max's camera works like a real-world camera, as do the other 3D applications.
Adobe's After Effects 5.5 offers real-world settings, but, surprisingly, is not a true 3D application. Figure 2.9 shows the After Effects Camera panel, where you can visually see the camera lens settings, as well as specific aperture settings.
Figure 2.9 The After Effects 5.5 Camera panel is one of the more intuitive control areas available in software applications.
So what is focal length, and how does it work? Focal length is an optical term that means the distance, usually in millimeters, from the lens to the point of focus (the subject). The longer the focal length of a lens, the smaller its field or angle of view. Given that, a long telephoto lens, such as a 400mm, can view a small area only. This is not to be confused with how far the lens can see, only what it sees. For example, a camera lens with a 400mm focal length is twice as powerful, but has half the field of view, of a 200mm lens. On the flip side, a 20mm lens has a very wide angle of view (hence, it's called a wide-angle lens). You can very easily apply real-world camera lenses and focal lengths to your digital scenes simply by entering the desired values in your software application's camera control panel. (See Figures 2.10 and 2.11.) It's a lot easier than changing lenses!
Figure 2.10 In this 3D scene, the camera's focal length (its lens) was set to 120mm. You can see that the overall look is tight on a specific area of interest.
Figure 2.11 This is the same shot as the previous figure, but with the focal length set to a 35mm lens. The field of view is much wider.
In the digital environment, you can animate focal length to give your animation a very different look. This will be explained in detail in Chapter 6, "[digital] Directing."
Knowing when to use specific focal lengths is really up to you as a digital cinematographer. Choosing the right focal length, f-stop, and other camera settings is what a true cinematographer must decide for each production. As a 3D animator and digital cinematographer, you must decide when and how the right camera settings will be used. The project example throughout this book will be used to help you understand many different situations you can encounter.