Camera FOV vs Focal Length

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Camera FOV vs Focal Length

Camera FOV vs Focal Length

2005-05-09 - By Andre DeAngelis

Back

Reply: 1 2 3 4 5

Indeed it is.

Sounds so trivial but in practice it can trip you up.

Anyway, thanks for sharing your knowledge Marc

Andre

__ ____ ____ ____ ____ ____ ____

From: owner-xsi@(protected) [mailto:owner-xsi@(protected)] On Behalf
Of Marc Bourbonnais
Sent: Monday, May 09, 2005 2:07 PM
To: XSI@(protected)
Subject: Re: Camera FOV vs Focal Length

Well, it would depend on the final scan & crop of the images you're
working with. Usually you can see it with the aspect ratio. 1.33, 1.31,
1.37, 1.85... Some of the default values in the drop-down camera list
from XSI are a bit misleading and slightly off in my opinion.

Usually in film, the largest full gate you can get is from a 0.98" x
0.745" filmback window. Even this is usually cropped to 0.98" x 0.735"
to get the ancient 1.33 ratio. That's the Full Aperture in 35mm film.
The other typical formats are all crops inside that window.

Other classic values you might be working with are Academy aperture
(0.864" x 0.630", 1.37 ratio) or 1.85 framing (0.825" x 0.446", 1.85
ratio)

To be uber-picky, these last two framings should have a horizontal
optical shift, because of the sound stripe on the side of the film. Most
of the time I don't really bother with it.

Fun stuff, huh?

--
Marc Bourbonnais
3D TD
Hybride
(450)227-4245

-- -- Original Message -- --

From: Andre DeAngelis <mailto:andre.deangelis@(protected)>

To: XSI@(protected)

Sent: Monday, May 09, 2005 12:50 PM

Subject: RE: Camera FOV vs Focal Length

Thanks a lot for that Marc,

So for 35 mm camera the 3 values are properly set up then?

Andre

__ ____ ____ ____ ____ ____ ____

From: owner-xsi@(protected) [mailto:owner-xsi@(protected)]
On Behalf Of Marc Bourbonnais
Sent: Monday, May 09, 2005 11:51 AM
To: XSI@(protected)
Subject: Re: Camera FOV vs Focal Length

The relation between FoV, lens and aperture is correct in XSI.
It's the same trig relation between the 3 values.

The problem is the incorrect default aperture sizes for the HD
cams, so I can assume you are working with these types of plates.

The correct aperure size for high-end HD cams is 9.6mm x 5.4mm,
roughly 0.37795" x 0.2126". Not the default XSI values.

The magic trig relation is :

f = (0.5*Ap) / tan(0.5*FoV)

where

f = lens

Ap = aperture

FoV = Field of view angle

of course keep track of mm vs. inches, and horizontal vs.
vertical.

--
Marc Bourbonnais
3D TD
Hybride
(450)227-4245

-- -- Original Message -- --

From: Andre DeAngelis
<mailto:andre.deangelis@(protected)>

To: XSI@(protected)

Sent: Monday, May 09, 2005 10:58 AM

Subject: Camera FOV vs Focal Length

Hello All,

Can anyone point me in the direction of a reference that
explains the formula for the relation between FOV, Focal Length and Film
Aperture used by XSI's camera?

The presets in XSI's camera don't seem to correlate to
what the table the director has given us and I want to put a
script/plug-in to reproduce the table he has provided.

AD

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<meta name=Generator content="Microsoft Word 11 (filtered medium)">

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<div class=Section1>

Indeed it is.  <o:p>
</o:p>

<o:p> </o:p>

Sounds so trivial but in
practice it can trip you up.<o:p></o:p>

<o:p> </o:p>

Anyway, thanks for
sharing your knowledge Marc<o:p></o:p>

<o:p> </o:p>

Andre<o:p></o:p>

<o:p> </o:p>

<div>

<div class=MsoNormal align=center style='text-align:center'>

<hr size=2 width="100%" align=center tabindex=-1>

</div>

From:
owner-xsi@(protected) [mailto:owner-xsi@(protected)] On Behalf Of Marc Bourbonnais 
Sent: Monday, May 09, 2005 2:07 PM
 
To: XSI@(protected) 
Subject: Re: Camera FOV vs Focal
Length<o:p></o:p>

</div>

<o:p> </o:p>

<div>

Well, it would depend on the final scan & crop of the
images you're working with. Usually you can see it with the aspect ratio. 1.33,
1.31, 1.37, 1.85... Some of the default values in the drop-down camera list
from XSI are a bit misleading and slightly off in my opinion.<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

Usually in film, the largest full gate you can get is
from a 0.98" x 0.745" filmback window. Even this is usually
cropped to 0.98" x 0.735" to get the ancient 1.33 ratio. That's the
Full Aperture in 35mm film. The other typical formats are all crops inside that
window.<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

Other classic values you might be working with are Academy
aperture (0.864" x 0.630", 1.37 ratio) or 1.85 framing (0.825" x
0.446", 1.85 ratio)<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

To be uber-picky, these last two framings should
have a horizontal optical shift, because of the sound stripe on the side
of the film. Most of the time I don't really bother with it.<o:p>
</o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

Fun stuff, huh?<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

-- 
Marc Bourbonnais 
3D TD 
Hybride 
(450)227-4245<o:p></o:p>

</div>

<blockquote style='border:none;border-left:solid black 1.5pt;padding:0cm 0cm
0cm 4.0pt;
margin-left:3.75pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt'>

<div>

-- -- Original Message -- -- <o:p></o:p>

</div>

<div style='font-color:black'>

From:
 <a
href="mailto:andre.deangelis@(protected)" title="andre.deangelis@(protected)"
>Andre
DeAngelis</a> <o:p></o:p>

</div>

<div>

To: <a
href="mailto:XSI@(protected)" title="XSI@(protected)">XSI@(protected)</a>
<o:p></o:p>

</div>

<div>

Sent: Monday, May 09,
2005 12:50 PM<o:p></o:p>

</div>

<div>

Subject: RE: Camera FOV vs
Focal Length<o:p></o:p>

</div>

<div>

<o:p> </o:p>

</div>

Thanks a lot for that
Marc,<o:p></o:p>

<o:p> </o:p>

So for 35 mm camera the 3
values are properly set up then?<o:p></o:p>

<o:p> </o:p>

Andre<o:p></o:p>

<o:p> </o:p>

<div>

<div class=MsoNormal align=center style='text-align:center'>

<hr size=2 width="100%" align=center tabIndex=-1>

</div>

From:
<a href="mailto:owner-xsi@(protected)">owner-xsi@(protected)</a>
[mailto:owner-xsi@(protected)] On Behalf Of
Marc Bourbonnais 
Sent: Monday, May 09, 2005 11:51
AM 
To: <a
href="mailto:XSI@(protected)">XSI@(protected)</a> 
Subject: Re: Camera FOV vs Focal
Length<o:p></o:p>

</div>

<o:p> </o:p>

<div>

The relation between FoV, lens and aperture is correct in
XSI. It's the same trig relation between the 3 values.<o:p></o:p>


</div>

<div>

 <o:p></o:p>

</div>

<div>

The problem is the incorrect default aperture sizes for the
HD cams, so I can assume you are working with these types of plates.<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

The correct aperure size for high-end HD cams is 9.6mm x
5.4mm, roughly 0.37795" x 0.2126". Not the default XSI values.
<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

The magic trig relation is :<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

f = (0.5*Ap) / tan(0.5*FoV)<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

where <o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

f = lens<o:p></o:p>

</div>

<div>

Ap = aperture<o:p></o:p>

</div>

<div>

FoV = Field of view angle<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

of course keep track of mm vs. inches, and horizontal vs.
vertical.<o:p></o:p>

</div>

<div>

 <o:p></o:p>

</div>

<div>

-- 
Marc Bourbonnais 
3D TD 
Hybride 
(450)227-4245<o:p></o:p>

</div>

<blockquote style='border:none;border-left:solid black 1.5pt;padding:0cm 0cm
0cm 4.0pt;
margin-left:3.75pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt'>

<div>

-- -- Original Message -- -- <o:p></o:p>

</div>

<div style='font-color:black'>

From:
 <a
href="mailto:andre.deangelis@(protected)" title="andre.deangelis@(protected)"
>Andre
DeAngelis</a> <o:p></o:p>

</div>

<div>

To: <a
href="mailto:XSI@(protected)" title="XSI@(protected)">XSI@(protected)</a>
<o:p></o:p>

</div>

<div>

Sent: Monday, May 09,
2005 10:58 AM<o:p></o:p>

</div>

<div>

Subject: Camera FOV vs
Focal Length<o:p></o:p>

</div>

<div>

<o:p> </o:p>

</div>

Hello All,<o:p></o:p>

<o:p> </o:p>

Can anyone point me in the direction of a reference
that explains the formula for the relation between FOV, Focal Length and Film
Aperture used by XSI’s camera?<o:p></o:p>

<o:p> </o:p>

The presets in XSI’s camera don’t seem to
correlate to what the table the director has given us and I want to put a
script/plug-in to reproduce the table he has provided.<o:p></o:p>


<o:p> </o:p>

AD<o:p></o:p>

</blockquote>

</blockquote>

</div>

</body>

</html>