Depending on the projection type some of the parameters are required, some are optional and some aren't used. If no projection type is given the perspective projection will be used (pinhole camera). If no camera is specified a default camera is used.

Regardless of the projection type all cameras use the "location", "look_at", "right", "up", "direction", and "sky" keywords to determine the location and orientation of the camera. Their meaning differs with the projection type used. A more detailed explanation of the camera placement follows later.

The aperture setting determines the depth of the sharpness zone. Large apertures give a lot of blurring, while narrow apertures will give a wide zone of sharpness. Note that, while this behaves as a real camera does, the values for aperture are purely arbitrary, and are not related to f-stops.

The center of the "zone of sharpness" is the focal_point vector (the default focal_point is <0,0,0>).

The blur_samples value controls the maximum number of rays to use for each pixel. More rays give a smoother appearance, but is slower, although this is controlled somewhat by an adaptive mechanism that stops shooting rays when a certain degree of confidence has been reached that shooting more rays would not result in a significant change.

The confidence and variance variables control the adaptive function. The confidence value is used to determine when the samples seem to be "close enough" to the correct color. The variance value specifies an acceptable tolerance on the variance of the samples taken so far. In other words, the process of shooting sample rays is terminated when the estimated color value is very likely (as controlled by the confidence probability) near the real color value.

Since the confidence is a probability its values can range from 0 to 1 (the default is 0.9, i.e. 90%). The value for the variance should be in the range of the smallest displayable color difference (the default is 1/128).

Larger confidence values will lead to more samples, slower traces and better images. The same holds for smaller variance thresholds.

By default no focal blur is used, i.e. the default aperture is 0 and the default number of samples is 0.

The location is simply the X, Y, Z coordinates of the camera. The camera can be located anywhere in the ray tracing universe. The default location is <0, 0, 0>. The look_at vector tells POV-Ray to pan and tilt the camera until it is looking at the specified X, Y, Z coordinate. By default the camera looks at a point one unit in the +Z direction from the location.

The look_at specification should almost always be the last item in the camera statement. If other camera items are placed after the look_at vector then the camera may not continue to look at the specified point.

This tells POV-Ray to roll the camera until the top of the camera is in line with the sky vector. Imagine that the sky vector is an antenna pointing out of the top of the camera. Then it uses the "sky" vector as the axis of rotation left or right and then to tilt up or down in line with the "sky" vector. In effect you're telling POV-Ray to assume that the sky isn't straight up. Note that the sky vector must appear before the look_at vector.

The sky vector does nothing on its own. It only modifies the way the look_at vector turns the camera. The default value for sky is <0, 1, 0>.

The default value is direction <0, 0, 1>

The length of the direction vector determines the field of view for the perspective projection. It is the distance from the camera location to the imaginary "view window" that you are looking through. A short direction vector gives a wide angle view while a long direction gives a narrow, telephoto view. You should be careful with small direction vector lengths, i.e. large viewing angles. You may experience distortion on the edges of your images. Objects will appear to be shaped strangely. If this happens, move the location back and make the direction vector longer or decrease the viewing angle.

If you are using the ultra wide angle, panoramic or cylindrical projection you should use a unit length direction vector to avoid strange results.

The length of the direction vector doesn't matter if one of the following projection types is used: orthographic, fisheye, or omnimax.

or the "look_at" parameter (in combination with "location"). The directions of an explicitly specified right and up vector will be overridden by any following "look_at" parameter.

While some camera types ignore the length of these vectors others use it to extract valuable information about the camera settings. The following list will explain the meaning of the right and up vector for each camera type. Since the direction the vectors is always used to describe the orientation of the camera it will not be explained again.

Most computer video modes and graphics printers use perfectly square pixels. For example Macintosh displays and IBM S-VGA modes 640x480, 800x600 and 1024x768 all use square pixels. When your intended viewing method uses square pixels then the width and height you set with the +W and +H switches should also have the same ratio as the right and up vectors. Note that 640/480 = 4/3 so the ratio is proper for this square pixel mode.

Not all display modes use square pixels however. For example IBM VGA mode 320x200 and Amiga 320x400 modes do not use square pixels. These two modes still produce a 4/3 aspect ratio image. Therefore images intended to be viewed on such hardware should still use 4/3 ratio on their up and right vectors but the +W and +H settings will not be 4/3.

For example:

This specifies a perfectly square image. On a square pixel display like SVGA you would use +W and +H settings such as +W480 +H480 or +W600 +H600. However on the non-square pixel Amiga 320x400 mode you would want to use values of +W240 +H400 to render a square image.

This whole explanation needs work. DLR

The left-handed coordinate system.

This means that the +X direction is to the right. It is called a "left- handed" system because you can use your left hand to keep track of the axes. Hold out your left hand with your palm facing to your right. Stick your thumb up. Point straight ahead with your index finger. Point your other fingers to the right. Your bent fingers are pointing to the +X direction. Your thumb now points +Y. Your index finger points +Z.

To use a right-handed coordinate system, as is popular in some CAD programs and other ray tracers, make the same shape using your right hand. Your thumb still points up in the +Y direction and your index finger still points forward in the +Z direction but your other fingers now say the +X is to the left. That means that the "right" side of your screen is now in the -X direction. To tell POV-Ray to act like this this you can use a negative X value in the "right" vector like this:

Since X increasing to the left doesn't make much sense on a 2D screen, you now rotate the whole thing 180 degrees around by using a positive Z value in your camera's location. You end up with something like this.