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On Sun, 28 Jan 2001 17:39:49 -0600 Maan M. Hamze wrote in p.programming:
>Although the value of keyword Aperture in povray is random and is not
>related to
>f-stops (I wish it was), is there any rough correlation that one can draw
>between povray keyword Aperture on one hand, and a camera actual focal
>length and f-stops on the other hand?
>Maan
Hi, Maan. Your question is best asked in povray.newusers, which
followups to this post will be directed to. P.general would also have
been a relevant group, since the questions weren't specific to the
Windows version of POV-Ray but pertains to all platforms.
The group povray.programming is actually a discussion area for the c
source code that developers use to build and compile the actual POV-Ray
rendering engine.
There is an article in p.announce.f-a-q group entitled, "Welcome To
the POV-Ray News Groups". This article explains where to post questions
in the most relevant groups.
--
Alan - ako### [at] povray org - a k o n g <at> p o v r a y <dot> o r g
http://www.povray.org - Home of the Persistence of Vision Ray Tracer
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> On Sun, 28 Jan 2001 17:39:49 -0600 Maan M. Hamze wrote in p.programming:
>
> >Although the value of keyword Aperture in povray is random and is not
> >related to
> >f-stops (I wish it was), is there any rough correlation that one can draw
> >between povray keyword Aperture on one hand, and a camera actual focal
> >length and f-stops on the other hand?
There must be, if only a "rough" estimation anyway. Just a guess, but I think
the focal blur in POV-Ray is only linear. I don't know.
Render a simply test scene based on a real life photo and I think you'd get a
correlation with some math involved. Think the main difference is that f-stops
aren't linear to the focus.
Bob H.
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I am going to study this further this weekend along with the inc file that I
was refered to in this thread.
Maybe I can come up with a correlation between f-stops and Aperture. The
f-stops are related mainly to control of depth of field. Where one area is
in focus with the background and foreground thrown out of focus. Mainly if
you focus on a point, one third of the line in front of the point and two
thirds of it behind the point will be in focus (the line being the total
line in focus or the depth of field). One other variable is the Hyper Focal
setting where ALL is in focus to infinity.
so it will be some interesting work.
Maan
"Bob H."
<per### [at] aolcom?subject=PoV-News:%20&body=Relating%20to%20POV-Ray:>
wrote in message news:3a755a2e@news.povray.org...
> > On Sun, 28 Jan 2001 17:39:49 -0600 Maan M. Hamze wrote in p.programming:
> >
> > >Although the value of keyword Aperture in povray is random and is not
> > >related to
> > >f-stops (I wish it was), is there any rough correlation that one can
draw
> > >between povray keyword Aperture on one hand, and a camera actual focal
> > >length and f-stops on the other hand?
>
> There must be, if only a "rough" estimation anyway. Just a guess, but I
think
> the focal blur in POV-Ray is only linear. I don't know.
> Render a simply test scene based on a real life photo and I think you'd
get a
> correlation with some math involved. Think the main difference is that
f-stops
> aren't linear to the focus.
>
> Bob H.
>
>
>
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"Maan M. Hamze" wrote:
>
> I am going to study this further this weekend along with the inc file that I
> was refered to in this thread.
> Maybe I can come up with a correlation between f-stops and Aperture. The
> f-stops are related mainly to control of depth of field. Where one area is
> in focus with the background and foreground thrown out of focus. Mainly if
> you focus on a point, one third of the line in front of the point and two
> thirds of it behind the point will be in focus (the line being the total
> line in focus or the depth of field). One other variable is the Hyper Focal
> setting where ALL is in focus to infinity.
> so it will be some interesting work.
http://www.google.com/search?q=%22circle+of+confusion%22+%22depth+of+field%22+%22hyperfocal+distance%22
--
Best regards,
Tor Olav
mailto:tor### [at] hotmailcom
http://www.crosswinds.net/~tok
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"Maan M. Hamze" <mmh### [at] pleiadesnet> wrote in message
news:3a7a04fd@news.povray.org...
> Maybe I can come up with a correlation between f-stops and Aperture. The
> f-stops are related mainly to control of depth of field. Where one area is
> in focus with the background and foreground thrown out of focus. Mainly if
> you focus on a point, one third of the line in front of the point and two
> thirds of it behind the point will be in focus (the line being the total
> line in focus or the depth of field).
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.
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Thanks Tor, I got some interesting links. I personally have lots of books
on the subject that goes into detail and formulations. But the links are a
good addition.
Maan
"Tor Olav Kristensen" <tor### [at] onlineno> wrote in message
news:3A7B136B.F3770084@online.no...
>
> "Maan M. Hamze" wrote:
> >
> > I am going to study this further this weekend along with the inc file
that I
> > was refered to in this thread.
> > Maybe I can come up with a correlation between f-stops and Aperture.
The
> > f-stops are related mainly to control of depth of field. Where one area
is
> > in focus with the background and foreground thrown out of focus. Mainly
if
> > you focus on a point, one third of the line in front of the point and
two
> > thirds of it behind the point will be in focus (the line being the total
> > line in focus or the depth of field). One other variable is the Hyper
Focal
> > setting where ALL is in focus to infinity.
> > so it will be some interesting work.
>
>
http://www.google.com/search?q=%22circle+of+confusion%22+%22depth+of+field%2
2+%22hyperfocal+distance%22
>
>
> --
> Best regards,
>
> Tor Olav
>
> mailto:tor### [at] hotmailcom
> http://www.crosswinds.net/~tok
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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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"Sander" <san### [at] stolscom> wrote in message
news:MPG### [at] NEWSPOVRAYORG...
>
> I don't know about POV: this is not the same thing as PPB, is it?
Lost me. I couldn't figure what PPB is.
> 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...
Interesting. Very unlike optical microscopes then I guess (of course, no
kidding).
I was trying to remember if the post_process blurring of MegaPov had a range of
focus but it's been awhile since I used that. Oh, hey, is that what you were
saying? PPB= post process blur...?
Anyway, the singular planar(?) focus of focal blur certainly isn't like what is
seen in photographs but is a lot like what is seen in binoculars and such. I
know you're right about the inability of photos to show a precision comparable
to a ray trace. Still, always seems a focusable depth can be attained whereas
it's not in POV.
Bob H.
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