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The Beginner's Guide to CG

Part 1: camera basics By Stephen Schleicher
I usually spend an hour each day cruising the Internet visiting various sites that showcase the works of talented, and sometimes not so talented, 3D artists. I have seen some amazing work done in virtually every animation package on the market today, ranging from character modeling and animation to technical and mechanical works of art.

While these images are often composed very nicely, it is sometimes very obvious that the animator is using the default setting on the camera and moving it closer or further away from the subject to get proper framing. This is all well and good, but if an animator/artist wants to create shots that mimic real world cameras, then he needs to know a little bit about lenses and duplicate those lenses in his scenes. In this first installment, Iíll define the different types of lenses and discuss depth of field so your CG images go from "blah" to "Woo Hoo!"

Telephoto, wide ... whatís the diff?
Every 3D package gives the user the option to control the type of lens being used in scene. However, beginning (and even some intermediate and advanced) users can get confused when looking at the many options available; Zoom Factor, Focal Length, Horizontal and Vertical FOV (Field of View), Depth of Field, Aperture and so on. If you are not familiar with the terms, donít worry. There are two things to remember about all of these terms: First, many of these terms mean basically the same thing; and second, all of these terms are interdependent on each other.

Focal length
Letís start off by talking about focal length. Focal length is determined by the distance from the optical center of the lens to the point where all light rays converge to form a perfectly focused picture. This length is measured in millimeters and, depending on how long or short this measurement is, will determine what type of lens you are using. For the purpose of this discussion, all camera references will be based on a 16 mm camera. Every 3D package I have seen usually has various presets for the type of camera being used, including 16 mm, super 8, IMAX and various CCD chip cameras. For the purposes of demonstration, I am using a default scene from NewTekís LightWave 3D to illustrate ideas and concepts.

So, we have an idea of how Focal Length is measured, but how does that relate to what we see?

Letís start with a normal lens. We call it a normal lens because it produces an image that is similar to what the human eye sees. The focal length for normal lenses generally fall in the 22 mm to 25 mm range. If you open your 3D program, you will probably find that the default camera is set somewhere in this range. This is fine if you are trying to emulate "normal" vision, but this generally produces a static or average image (image 1). I would estimate that 75 percent to 80 percent of the 3D animations and images I see today are from people who are using this default setup.

Image 1. In a normal lens, the focal length falls around 22 mm to 25 mm and
produces an image similar to what our eye sees.

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