Was the Hubble telescope too convave or convex?

The primary mirror had been ground too flat at the edge (by 2 µm; i.e. 1/50th of the width of human hair!), producing spherical aberration (light at the edge of the mirror is focused at a different point as the light in the center of the mirror), actually visible as flawed images.

The Cassegrain reflector (= the primary mirror) actually is a concave system.