Which of the following statements regarding the Sag lens formula is correct?

The statement regarding the Sag lens formula that is correct is that it only applies to lenses with spherical curves. This formula is specifically designed to calculate the sagita, or the depth of a lens at its center, based on the radius of curvature and the diameter of the lens. The formula is most accurate when assessing lenses that have uniform curvature typical of spherical lenses.

Spherical lenses are characterized by their consistent curvature across their entire surface, which allows the Sag formula to be reliably applied. On the other hand, cylindrical lenses have different curvatures along two perpendicular axes, meaning that the Sag formula cannot be used in the same straightforward manner as it does with spherical lenses. Thus, while the Sag formula is valuable for specific contexts, it is not as broadly applicable as the statement implies in relation to all lens types.