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Hi!
POV-Ray uses the horizontal angle to determine the clipping. Does somebody
know how to calculate the focal length when only the horizontal angle is
given?
Regards,
Andreas
--
http://www.render-zone.com
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From: Christoph Hormann
Subject: Re: How to calculate the focal length?
Date: 29 Mar 2003 09:05:19
Message: <3E85A858.67B58C91@gmx.de>
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Andreas Kreisig wrote:
>
> Hi!
>
> POV-Ray uses the horizontal angle to determine the clipping. Does somebody
> know how to calculate the focal length when only the horizontal angle is
> given?
>
The relation between camera angle and focal length obviously depends on
the film/sensor size of the camera.
See for example:
http://www.colloquial.com/photo/formats.html
http://www.mat.uc.pt/~rps/photos/angles.html
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
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Andreas Kreisig wrote:..
> Hi!
>
> POV-Ray uses the horizontal angle to determine the clipping. Does somebody
> know how to calculate the focal length when only the horizontal angle is
> given?
>
> Regards,
> Andreas
>
>
I suppose that what you mean by "focal length" is the direction vector
(the distance between the focal point and the screen). The relation
between the horizontal angle and the focal length (direction) can be
found in the PovRay Help section 6.4.1.
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From: Andreas Kreisig
Subject: Re: How to calculate the focal length?
Date: 29 Mar 2003 12:05:06
Message: <3e85d242@news.povray.org>
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HermanS wrote:
> Andreas Kreisig wrote:..
>> Hi!
>>
>> POV-Ray uses the horizontal angle to determine the clipping. Does
>> somebody know how to calculate the focal length when only the horizontal
>> angle is given?
>>
>> Regards,
>> Andreas
>>
>>
> I suppose that what you mean by "focal length" is the direction vector
> (the distance between the focal point and the screen). The relation
> between the horizontal angle and the focal length (direction) can be
> found in the PovRay Help section 6.4.1.
Hm, I meant the focal length of a virtual lens. This is not the same as the
distance between the focal point and the screen.
Regards,
Andreas
--
http://www.render-zone.com
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From: Andreas Kreisig
Subject: Re: How to calculate the focal length?
Date: 29 Mar 2003 12:13:33
Message: <3e85d43c@news.povray.org>
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Christoph Hormann wrote:
>
>
> Andreas Kreisig wrote:
>>
>> Hi!
>>
>> POV-Ray uses the horizontal angle to determine the clipping. Does
>> somebody know how to calculate the focal length when only the horizontal
>> angle is given?
>>
>
> The relation between camera angle and focal length obviously depends on
> the film/sensor size of the camera.
Yes, but my problem is that POV-Ray has no film or sensor size. The
background: I want to use the same camera settings in Blender than in POV.
POV-Ray uses the (horizontal) 'angle' directive, Blender uses a focal
length similar to a real camera. I know that the angel of the camera has 25
degrees so I need the corresponding focal length.
Impossible?
Regards,
Andreas
--
http://www.render-zone.com
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From: Christoph Hormann
Subject: Re: How to calculate the focal length?
Date: 29 Mar 2003 12:24:16
Message: <3E85D6FA.1F6DBC09@gmx.de>
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Andreas Kreisig wrote:
>
> Yes, but my problem is that POV-Ray has no film or sensor size. The
> background: I want to use the same camera settings in Blender than in POV.
> POV-Ray uses the (horizontal) 'angle' directive, Blender uses a focal
> length similar to a real camera. I know that the angel of the camera has 25
> degrees so I need the corresponding focal length.
Why don't you read what i wrote. The viewing angle of a (photographic)
camera with a certain focal length depends on what film format or sensor
it uses. I don't know how Blender calculates a camera angle from a given
focal length but it has to assume a certain film format for that.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
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From: Marc Jacquier
Subject: Re: How to calculate the focal length?
Date: 29 Mar 2003 13:21:30
Message: <3e85e42a@news.povray.org>
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3E85D6FA.1F6DBC09@gmx.de...
> I don't know how Blender calculates a camera angle from a given
> focal length but it has to assume a certain film format for that.
>
> Christoph
>
I don't know more about blender but usually it is spoken of a 35mm (36x24mm
image) film in that discussions.
so as angle means horizontal angle :
Angle of View = 2 * ArcTan(Size/ (2 * Focal Length * (1 + Magnification)))
assuming the lense is normal (not a macro one), Magnification can be
considered as 0.
so
Angle of View = 2 * ArcTan(Size/ (2.Focal Length ))
and
Focal Length=(Size/2)*cotan(Angle/2)
But my maths are far away in the mists of ages so I can be wrong
Marc
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From: Christoph Hormann
Subject: Re: How to calculate the focal length?
Date: 29 Mar 2003 13:54:10
Message: <3E85EC0D.101EA7AD@gmx.de>
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Marc Jacquier wrote:
>
> I don't know more about blender but usually it is spoken of a 35mm (36x24mm
> image) film in that discussions.
> so as angle means horizontal angle :
> Angle of View = 2 * ArcTan(Size/ (2 * Focal Length * (1 + Magnification)))
That's exactly what the first of the links i posted says too. But there
is no reason why it has to be a 35mm film the calculations are based on.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 28 Feb. 2003 _____./\/^>_*_<^\/\.______
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