MEL - Angle of View

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  02 February 2013
MEL - Angle of View

Hi there,
is there any way to read the Angle of View (instead of the Focal Lenght) of a camera via MEL or and expression? It seems there is no getAttr or setAttr for it.

If this is not possible, how would I calculate the AOV from the Focal Length?

Cheers, Florian
  02 February 2013

You need to known factors: the focal length f and the size of the camera aperture d (actually the film/ccd sensor size, but in Maya this would be the effective aperture). By default, aperture is equal to a 35mm image. While there are actually 3 angles of view (vertical, horizontal and diagonal), Maya only shows us the horizontal angle, as calculated by the following formula:

angle of view = 2 x atan(d / (2xf));


float $d = 35;  // film width
float $f = 50;  // focal length
float $ratio = $d / (2 * $f);
float $a = 2 * atan($ratio); // angle in radians
$a = rad_to_deg($a); // angle in degrees

In Python:
import math

def aov(d,f):
	a = 2 * math.atan(float(d) / (2*float(f)))
	a = math.degrees(a)
	return a

a = aov(35,35)
print a

Note that Maya seems to use some rounding internally, so the resulting values are not exactly identical.
  02 February 2013
Vielen Dank.
Gonna try it tomorrow.

Cheers, Florian
  02 February 2013
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