Tech Specs of Built-in iSight Camera of MacBook (13-inch, Aluminum, Late 2008)
What is recommended is doing a camera calibration yourself, using OpenCV for instance, to get reliable figures.
http://docs.opencv.org/2.4/doc/tutorials/calib3d/camera_calibration/camera_calibration.html

It is not very complicated, just print out the chessboard pattern, tweak the xml file which has input data for information about the test pattern and also the xml for input images(if you plan on using images, instead of live video through your webcam, I recommend the latter) 
Run the sample as it is, following the instructions for keyboard prompts (hold up pattern, press 'g' to start calibration once you see detected lines, esc to exit).