code: function ( focalLength ) {
  
  		// see http://www.bobatkins.com/photography/technical/field_of_view.html
  		var vExtentSlope = 0.5 * this.getFilmHeight() / focalLength;
  
  		this.fov = THREE.Math.RAD2DEG * 2 * Math.atan( vExtentSlope );
  		this.updateProjectionMatrix();
  
  	}
docs: Sets the FOV by focal length in respect to the current .filmGauge.
  
  The default film gauge is 35, so that the focal length can be specified for
  a 35mm (full frame) camera.
  
  Values for focal length and film gauge must have the same unit.