R1 in a lens is positive …

The sign conventions for the radii of curvature (R1 and R2) for lenses are as follows: 1. **Convex Lens (Diverging Lens)**: - R1 (the radius of curvature of the first surface) is considered positive if the center of curvature is on the same side as the incident light (opposite to the direction of incoming light). - R2 (the radius of curvature of the second surface) is considered negative. 2. **Concave Lens (Converging Lens)**: - R1 (the radius of curvature of the first surface) is considered negative. - R2 (the radius of curvature of the second surface) is considered positive if the center of curvature is on the same side as the incident light (opposite to the direction of incoming light). These conventions are used in lens formula and mirror formula calculations to determine the sign of focal lengths and object distances.