Focal Length Viewing Angle Index of Elasticity Image Area 600mm 4.0 0.007 2.00 400mm 6.0 0.015 2.00 180mm 13.5 0.078 2.03 105mm 23.0 0.230 2.07 50mm 46.0 1.000 2.33 28mm 75.0 3.268 2.82 20mm 95.0 6.382 3.41 15mm 110.0 11.320 4.36 The trigonometric calculations -- essentially, tangents to angles of two adjacent right triangles -- are straightforward. Thought you might have interest in this. Also, my apologies for the bad formatting of the table - …Robert |