Does getVerticalViewAngle() give actual Camera Angle Field Of View(CAFOV) value?

<p>I am utilizing a built in function named "getVerticalViewAngle()" to get the Vertical View Angle of Android Device Camera. The above function returns "63.8146" degrees as the Vertical Angle.<br>

Now if I use the tablet on a tripod so that tilt is eliminated (Keeping tablet camera lens height as 900mm) and capture a picture of a wall at a distance of 1500mm, then 1800mm of the wall(vertical) is included within the picture. Calculating the Vertical Angle based on above scenario yields 61.9275 degress which is not equivalent to 63.8146.</p>

<p><img src="http://windowmaker.com/distancecalc.jpg" alt="" width="500" height="500" /><br>

Can anyone please explain why there is difference between Angle values?</p>

<p>In case anyone is interested, the OP asked this question on other websites /forums and got a very nice answer here:<br>

http://photo.stackexchange.com/questions/61695/does-getverticalviewangle-give-actual-camera-angle-field-of-viewcafov-value</p>

<p>Tom M</p>

From the link: "However normally the focal length gets shorter the closer you focus,"

 

This is incorrect. Focal length gets longer as you focus closer, reducing the angle of view.

<p>I think the part of the answer in that link, indicating that a tablet isn't a scientific nor calibrated device is the real reason. In fact, I find the fact that the difference is just 2 degrees already quite astonishingly close. Tablets are mass production devices, sold as cheap as possible; I wouldn't expect much accuracy from it for applications such as these.</p>