Trilobite Paciphacops - left eye

Multi-focus (20 exposures) image of the fossilised schizochroal eye of a Devonian trilobite (345-395 million years old). The compound eye (pseudo-cylinder) measures approximately 5mm in diameter.

The lenses are formed of calcite (calcium carbonate, CaCO_3) with the crystallographic 'c'-axis aligned with the axis of each lenslet. This is the direction in which the light is not doubly-refracted, resulting in a clear image in that direction. By forming the inner part of the lens with magnesium-infiltrated calcite, the 'doublet' lens suffered much less from spherical aberration than a simple pure-calcite lens.

And we reinvented spherical aberration with the Hubble Space Telescope - but also cured it!



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