"Ross" <rli### [at] everestkcnet> wrote:
> the FAQ at tag.povray.org says this in comparing MegaPOV postprocess focal
> blur with POV's internal focal blur:
>
> "For example, think that you have a red box in front of a green box so that
> one of their edges coincide in the final image (the green box is located
> behind the red box so that it's not seen in the image, but if you moved the
> camera just a bit in the right direction the edge of the green box would
> become visible). Now use focal blur so that the focal point is at the edge
> of the green box: Part of the green box appears from behind the blurred red
> box!
> This is not possible with the post-process focal blur. "
>
> Is this based on a real world physical model? i'm no photographer, but this
> sounds counter-intuitive to real vision (atleast with a single lense?
> atleast my intuition?). i tried searching the news groups for things like
> "focal blur physical model" and several variations, but nothing popped out
> at me.


Well, I haven't tried that example in Pov, so I don't know how much of that
'bleed' is apparent, but yes, that does happen with a real camera, at least
when the objects are close enough to the camera.  DOF is dependent on lens
focal length, distance to film plane, & aperture size, so the further away
the focal point in relation to the focal length the less the effect. When
using a macro lens at very close distances its quite noticable.

Here's an explanation of it, look at the diagram about "circle of
confusion", it should help:
http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/950/depth-of-field.html

If you look at some macro photography sites you should see some examples.

RG

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