A spherical generator is used to produce a -15.00D surface on glass of refractive index 1.80. The diameter of the cutting tool is 80mm and the radius of the cutting surface is 4mm. What is the angle between the axis of the tool and the axis of the lens?
sinθ =R(cutting surface)/R(cutting tool) =4/40 =0.1
θ=sin⁻¹0.1 =5.7°