Depth of Field
Depth of field defined is that area in front of and behind the subject that is in relatively sharp focus. Everything outside of that area falls out of focus. Until now, all images in this article have been rendered without any depth of field. In a sense, they have the Infinity focus setting turned on and everything is in perfect focus. Depth of field is important in that helps create aesthetically pleasing images.

It is also important to note that depth of field extends approximately twice as far behind the subject as it does in front of the subject. This basically means that that area behind your subject will be in relatively sharp focus further back than that area in front of your subject.

Depth of field is determined by three factors:
1. The focal length. The shorter the focal length (the wider the shot), the deeper the depth of field. As the focal length increases the depth of field decreases.

Focal Length has a big impact on depth of field, by making it deep, with a wide angle lens, or shallow with a telephoto lens.

2. F-stop. The smaller the lens opening, the deeper the depth of field. Opening the iris decreases the depth of field.
3. Camera to subject distance. The larger the distance between the camera and the subject, the greater the depth of field. The shorter the distance, the shallower the depth of field.

Because we are not being application specific in this article, there are different ways depth of field is controlled in each package. In some programs, you must manually figure out how far away the subject is from the camera and once that distance is entered, the application will automatically determine how deep the depth of field is based on focal length and f-stop. Other programs, will give you the option to drag out a marker to your subject, and then have user definable settings for depth settings.

Let's see how focal length affects depth of field. In images 8, 9 and 10 I have "focused" my virtual camera on the white pawn. Because we are duplicating previous images, camera to subject distance also changes, which also plays a roll in how deep or shallow the depth of field in each shot is.

For these examples, the 3D package I am using takes f-stop into consideration in calculating depth of field. If I wanted to increase or decrease the depth of field, I would change the f-stop setting. In images 11 and 12, I have used a very narrow lens and a short camera to subject distance to achieve a very shallow depth of field. In the first image, I used a standard f-stop setting of f/4. You can see that foreground and background objects are out of focus. In the second image, I used an f-stop setting of f/22. This results in a much deeper depth of field, with almost everything in focus.

It should also be pointed out that in order to access the depth of field settings in your 3D program, you will probably have to increase the anti-aliasing of your program. The better the depth of field blurring, the higher the anti-aliasing, and the longer your render times.

If you do not want to deal with depth of field in your animation program, there are numerous plug-ins on the market today that will simulate depth of field without the huge render times. Also there are other ways to simulate or fake depth of field. The first way would be render everything in different layers and then apply blurring in a compositing package. Another would be if you animation package can store z-buffer information in the rendered image that you could then manipulate in another program. It should be pointed out that the render times for the images in this article varied between 1 and 2 minutes at extreme anti-aliasing on a PIII 600Mhz machine

Hopefully, this look at the different types of lenses and how depth of field can affect your rendered images will give you a good starting point to begin to experiment and make your rendered images go from ordinary to extraordinary. In part 2 we will discuss composition and how sometimes placing the camera in a different location can change the feel of a scene dramatically.