Alain <kua### [at] videotronca> wrote:
> In POV-Ray, there is no real diameter for the camera and no real focal
> length. Unless defined otherwise, it's an ideal pinhole camera.
>
> When you want to enable focal blur, you need to define an arbitrary
> aperture and set a focal point. The effective focal plane is
> perpendicular to the line going from the camera to the focal point.
> There is no concept of f stops.
>
> The area of sharpness depend on the ratio between the aperture and the
> distance from the camera location to the focal point
>
> Sample camera with focal blur :
>
> camera{location -20*z
>   up y // default
>   direction z // default
>   right 4/3*x // default if version <= 3.7
>   aperture 0.25
>   focal_point <0,0,0> // default
>   blur_samples 100// maximum number of samples to take.
>   confidence 0.99 //Must be less than 1
>   variance 1/256 //must NOT be zero
> }
>
> This setup result in a camera that is close to a camera at f80 with an
> horizontal field of view of about 40°.
> The samples are taken in a roughly circular pattern.
> You can set a minimum number of samples by using two values for
> blur_samples :
> blur_samples 12, 100
> The samples are simply averaged to get the final value for the current
> pixel been rendered.

I have found an attached `patio_stereo_near2.pov` file with something like this:

    camera{
      location cam_pos+half_interocular*dir_right*(clock*2-1)
      direction
cam_dir-vlength(cam_dir)*dir_right*half_interocular/convergence_dist*(clock*2-1)
      up        cam_up
      right     cam_right
      focal_point fountain_pos
      aperture 10     // twice much blurring
      blur_samples 800      // many samples, high quality image
      variance 0. // 0001 // see pov-ray soc on focal blur
    }

So it means that the focal plane is perpendicular to `direction` and goes
through `focal_point`.
My goal is to find the diameter of the point spread function (also called the
circle of confusion https://en.wikipedia.org/wiki/Circle_of_confusion) with
respect to depth.

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