I would like to make a Schupman telescope. The objective is a double convex lens. 4 inches in diameter. R1 radius is 27.133 inches, R2 radius is 302.400 inches. I have never made a lens and am having problems understanding how to calculate the sagitta of R1 and R2. In the Edmund Optics sagitta calculator should I enter the radius as negative, since they are convex?

At the moment I am getting a smaller number for the sagitta of the lens with the longer radius, which does not seem to make sense.