Hi all,

From 6.4.3:

"The center of the zone of sharpness is specified by the  focal_point
vector. Objects close to this point are in focus and those farther from
that point are more blurred. The default value is  focal_point<0,0,0>."

This doesn't make sense to me.  Shouldn't you just have to define a
(scalar) distance from the camera for focal blur calculations?  The focal
point would then lie on the direction vector at the specified distance
from the camera.

A related question: If I specify focal_point<0,0,5>  *before* I specify
the location and look_at, do I end up with a focal point five units in
front of the camera?  Or is the focal_point an absolute position?

I hope you'll pardon all the questions; the documentation seems a bit
sparse on this point.

Many thanks,

	-Ed


-- 
// [Insert amazingly brief and obfuscated but somehow artistic
//  povray code here.]

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On Tue, 23 Jul 2002 22:21:30 -0500, Ed Jackson <eja### [at] iastateedu>
wrote:

>This doesn't make sense to me.  Shouldn't you just have to define a
>(scalar) distance from the camera for focal blur calculations?  The focal
>point would then lie on the direction vector at the specified distance
>from the camera.

Don't quote me on this, but I think the reason the focal point is not
a scalar is that thus the restriction of having it on the focal axis
is avoided. There are sometimes situations when you need this. I've
seen photos with their focal point way off the center - of course,
they were cropped off bigger photos to achieve the effect, but if you
want to do that in POV and have to render an image where you'll only
use 25% of it, it won't make much sense.

I guess that answers your questions.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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in news:pan### [at] iastateedu Ed Jackson
wrote: 

> Shouldn't you just have to define a (scalar) distance from the camera
> for focal blur calculations? 

Comming from photography this seems the locical way. But in POV-Ray 
there is one difference. If you'd had to set a focal point distance, 
you'd first have to calculate the distance from camera to subject. In 
the current situation you have to calculate noting, one glance at the 
scene gives you the location of the subject and thus the focal point. 
The exception is when you've put the subject in position by 
transformation.

 
> A related question: If I specify focal_point<0,0,5>  *before* I
> specify the location and look_at, do I end up with a focal point five
> units in front of the camera?

Have you tried?

Ingo

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"Peter Popov" <pet### [at] vipbg> wrote in message
news:tvisjust0rhrgpioij3s9h42p6djgf5bp0@4ax.com...
<snip>
> I've
> seen photos with their focal point way off the center - of course,
> they were cropped off bigger photos to achieve the effect,

You can gat this effect with some high-end cameras or lenses, although I do
not know how it is called in English. You need to be able to dis-align the
lens and the film (rotation and/or translation). I believe you can also
achieve this using an enlarger.

> but if you
> want to do that in POV and have to render an image where you'll only
> use 25% of it, it won't make much sense.

You can shear the camera to get the effect. See the shear.pov file in the
../scene/camera/ directory of pov 3.5. Don't forget to switch the vista
buffer off (-uv).



Povingly,


Philippe

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