Some marine organisms bear more than one lens; for instance the copepod "Pontella" has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, "Copilia"'s eyes have two lenses, arranged like those in a telescope. Such arrangements are rare and poorly understood, but represent an interesting alternative construction. An interesting use of multiple lenses is seen in some hunters such as eagles and jumping spiders, which have a refractive cornea (discussed next): these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.

Parabolic superposition
Overview
Multiple lenses
Spherical lensed eye