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.

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"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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"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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