> The direction vector set the reference plane of the image. Objects in
> front of that point appear larger and those beyond appear smaller. Along
> with the up and right vectors, it determine the field of view, not a
> focal length.
> The image plane is where the point computer by adding the camera's
> location and the direction vector, and is perpendicular to the direction
> vector. It's further modified if you use look_at or any transformation
> on the camera.

So if the direction vector is used to determine the field of view, how do I set
the 'f' value exactly? Suppose I've made a scene where I assume focal length=2
'units' and all objects, lens and image plane are set according to that.
How/Where do I set that in POVRay? As you must have seen in the .pov file, I say
"X units" from the camera. What I really want is that distance to be as "Y*f",
as in a multiplier of the f-value. How can I do that?

> The f/x is a ratio. Say the focal_point is 100 unit in front of the
> camera and you want an f/x of f100, you divide the distance between the
> camera and focal_point by your f/x, in this case, it gives an aperture of 1.
> Formula:
> vlength(Camera_Location - focal_point)/ (f/x)

Here the f/X I meant was like the f/1.4 or f/1.7 in real cameras. Supposing the
focal_point is X*f from the camera, and I want an aperture of f/2.0, what should
I set the 'aperture' parameter as? [Given that I know how to set 'f' value
first?]

> confidence is the probability that the resulting colour is correct.
> It's a statistical thing. It's recommended to always use a value smaller
> than 1.
> variance is how much you are willing to deviate from the exact colour.

I still didn't get how you say you know the 'correct' color. For computing
probabilities, that knowledge
is reqd. Is it approximated such that you keep adding the colors to the target
pixel, and when that pixel's
color stops changing much, you say you don't need more rays?

> You need to set focal_point.
> If left undefined, it may get located at the same place as the camera,
> or extremely far away.

But what does focal_point really do in the context of the tracing done?

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