Spherical aberration, wither reflective or refractive, can be a challenging concept for students accustomed to simpler optical problems.
- This animation by B. Surendranath draws out ray paths for both spherical and parabolic reflectors, to illustrate how spherical aberration of a mirror occurs.
https://www.surendranath.org/GPA/Optics/SphAber/SphAber.html
- This simulator by Tom Walsh at oPhysics uses Snell's Law calculations to show the spherical aberration of a convex lens. The curvature of either side and the indices of refection of both the lens and the outside medium can be adjusted independently.