In article <3a7be545$1@news.povray.org>, Bob H. says...
> Thing is I don't believe POV-Ray can focus on a range of distance and leave the
> rest out of focus.  I was going to mention that before but it's only my
> observation from past experience and not knowledge of the way POV works.
> Seems only the one plane, perpendicular to the camera to focal point line, is
> ever truly focused and all other distances are out of focus no matter how near
> to the focal plane and how small an aperture (of the POV kind).
> I take a lot of photographs but I don't know the science behind the photography
> as much as I'd like to.  Seems obvious though that a photo will have a range of
> focus whereas in POV it will not.
> Am I right? Anyone think the same thing?
> 
> Bob H.

I don't know about POV: this is not the same thing as PPB, is it?

As far as light optics is concerned: theoretically, a photograph would 
be in focus for one distance only. Several effects lead to the 
appearance of an acceptable sharpness of the image in a much wider 
range: as I recall for example the limited resolution of the emulsion 
(nowadays CCD or such things); same limitations to processing materials; 
resolution of the eye of the beholder; diffraction phenomena in the 
camera lens system; and probably more. The overall effect is that you 
are not able to see a difference in sharpness of the resulting picture. 

I have worked a great deal with electron optical systems, where the 
effective apertures  were in the order of .000001 radians. This had the 
peculiar effect that when you projected an image on a screen, it didn't 
matter anymore where you actually put the screen! Images were always 
sharp. This so-called depth of field ranged, for example, from 1 cm to 
10000 cm!! It had to do with the enormous magnifications used, for one 
thing...
-- 
Regards,  Sander

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