Well, the angle is a modifier. That means it doesn't really have a default
by itself; rather, it's based off of other things that have a default.

The camera parameters (for the default perspective camera) are:

location (default <0,0,0>)
direction (default <0,0,1>)
right (default <4/3,0,0>)
up (default <0,1,0>)

The angle is something you can set that changes the direction vector
depending on the value of the right vector. When you set the angle, it uses
the following formula to alter the direction vector:

direction_length =(1/2) * right_length / tan(angle/2)

So, in order to find the so called "default" of the angle, we simply solve
that equation for angle using the default of 1 as the direction_length and
4/3 as the right_length:

1 = 1/2*4/3 /tan(angle/2)
2/3 = tan(angle/2)
atan(2/3) = angle/2
angle = atan(2/3)*2

This turns out to be 1.176005 radians, or 67.380135 degrees.

Of course, you could have just found this answer by checking the
documentation =)

 - Slime
[ http://www.slimeland.com/ ]

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