OK, I admit I did the calculation in my head, and didn't check it. So... 8" f/2.8 => 44.8" ROC s = 4^2 / (2 * 44.8) => 0.1786" sagitta Volume of the cylinder = pi * 4^2 * 0.1786 => 8.97 The volume removed is about half this, or 4.48 cubic inches. Oh well. Anthony