Biconvex lenses are also called convexo-convex lenses and are mainly made
out of a special quality glass. Different types of biconvex-lenses exist
such as the planconvex-lens. The most common biconvex lens is the
symmetric-convex lens as used in this magnifier.
The biconvex lens is manufactured with identical convex surfaces each side
of the lens. The focal length is equal to the radius of the curvature.
Resulting from its perfect symmetry it produce images close to 1 and up to
a magnification of 8x. Biconvex lenses have positive focal lengths and form
both real and virtual images.
Aberrations such as coma, distortion, and chromatic aberration almost
exactly cancel out also due to the symmetry.