"gonzo" <rgo### [at] lansetcom> wrote in message
news:web.40e3c1a66037c979eac6f5ee0@news.povray.org...
> "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
>
>

Ahh, thank you much.

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