The compound eye of a fruit fly has some 700 facets. Each of these facets goes to eight photoreceptors. An extreme example of compound eye development can be found in Xenos pecki which is a parasite on paper wasps. Each eye of the male insect is made-up of only 50 lenses. However, each lens is 15 times as big as a fruit flies and contains 100 photoreceptors. Scientists estimate that up to 75% of this insects brain is given over to visual processing. This may be necessary if you only have an adult life span of two hours to find a suitable female.