Physics Photo of the
November 18, 2011
eyes are totally different from vertebrate eyes. Insect
eyes are compound
eyes. The compound eye consists of a hexagonal
arrangement of individual photoreceptors called ommatidia that cover the
hemisherical surface of each eye. Each ommatidium has a
lens at its opening that focuses the light onto the
photoreceptive nerve cell at its base that sends a
neurological signal to the animal's brain.
The image at right shows a close-up of the hexagonal
arrangement of the photo receptors.
Vertebrate eyes, on the other hand, consists of one lens that
focuses an image on the array of photo receptors on the retina
at the back of the eye. The main difference between
compound eyes and vertebrate eyes is that compound eyes have a
lens for each photoreceptor; vertebrate eyes have one lens for
all the photoreceptors. The evolutionary pressure for
the vertebrate eyes was a more compact eye for large
animals. If people had compound eyes, the eyes would
have to be many times our head sizes in order to see the same
field of view as insects.
Compound eyes can see images, but at much less resolution than
vertebrate eyes - principally due to the density of photo
receptors. A retina is much more efficient for high
resolution. Compound eyes are most likely more efficient
for small animals. Insect eyes can increase their
sensitivity to low light situations by combining the light
into adjacent receptors. This is analogous to some
digital cameras increasing light sensitivity by combining the
signal from adjacent pixels. The increase in sensitivity
comes with a trade-off of decreased resolution.
These pictures were taken with a "standard" zoom lens set at
55 mm focal length with no macro attachments. The
beautiful dragonfly had been found dead before being
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