Gary, perhaps a read of Leslie Stroebel's book might help you get a better handle on this. Manufacturers many times include data that is far more conservative than the actual performance of the lens. They do this because they are talking about the size of the image circle that offers the best image. In the reference you site, they state 52 degrees as the circle that has best resolution with the lens wide open, all lenses as you get closer to the edges loose resolution and preformance, so instead of having people bitch at them they publish very conservative data.Originally Posted by Gary892
You know how I find out about a lens coverage? I come to a forum like this and ask about the lens, most of the time people like Sandy, Clay, Thalmann, Don, etc know the answer. But if you really have to know how to make the math, Stroebel's book is the one to read.