TomDart opened this issue on Aug 23, 2005 ยท 7 posts
zahnfee posted Wed, 24 August 2005 at 3:20 AM
Here's my explanation, don't know if this helps: The equation to calculate the f-stop (aperture ratio) is focal length divided by the diameter of the lens. So the bigger the aperture/diameter of the lens at a given focal length the faster the lens.