# Talk:Field of View

in the formula

$FoV = 2 * atan \frac{35}{2 * Focal Length}$

The "35" should be some "length" because it is divided by a length, and should become unitless. Of course the length is the size of a standard negative: 35mm. If you want to "ignore units" as most americans like to do, it should note that "Focal length" is in mm. But more accurate is:

$FoV = 2 * atan \frac{35 mm}{2 * Focal Length}$

Should I just edit this into the main page, or should some discussion be held first? -- REW.

Just edit. Actually a "35mm" negative is 36mmx24mm in size. 35mm is the width of the entire film, including perforation etc. Since the formula is universal, I changed it to "size". (This error was pretty old, thanks for pointing it out) --Erik Krause 10:59, 11 June 2009 (UTC)