Acuity of compound eyes: Physical limitations and design

Abstract

The two fundamental limitations to resolving power of compound eyes are the wave (diffraction) and particle (photon noise) nature of light. By appreciating their interrelationship we gain insight into the design and limitation of eyes. In particular, we determine the dependence of eye design on the environmental light intensity. 1. The limitations to resolving power include: the intensity of light, angular motion, receptor grain, lens-pupil blur, finite diameter of rhabdom, and neural convergence. 2. Only those animals that are active in bright sunlight and normally have low angular velocity, profit by having some region of their eyes near the diffraction limit, i.e. DΔφ ≅ 0.58λ, where D is the facet diameter, Δφ the interommatidial angle and λ the wavelength in vacuum. If these conditions are not fulfilled, it is better to have a larger DΔφ. 3. The effect of an animal undergoing angular velocity u is equivalent to a reduction in light intensity by the amount exp-1.78(φtΔφ)2, where φt is the amount the animal turns in one integration time. Taking this into account, we present a possible explanation for Musca having DΔφ about 4.5 times greater than the diffraction limit. 4. Various strategies for dark-adaptation are considered with the conclusion that neural pooling combined with a widening of the acceptance angle is most effective for coping with reduced intensities. © 1977 Springer-Verlag.