Resolution of the eye. The angular resolution of the eye is determined by two factors, diffraction...

Resolution of the eye. The angular resolution of the eye is determined by two factors, diffraction (the Rayleigh criterion) and the density of photoreceptor cells within the retina. Here we investigate which one is more important in limiting resolution. The center circular area of the retina, roughly 0.3 mm in diameter, is called the fovea centralis and is the most sensitive part. The fovea has photoreceptor cells spaced about 1 ¾m apart center to center, compared with a spacing of 3 ¾m outside this region. The diagrams in Figure P25.61 illustrate how the angular resolution is limited by receptor density. Notice that for two objects to be resolved there must be an unstimulated cell between the image of the objects on the retina. In the upper diagram of Figure P25.61, the objects A and B are seen as one; in the lower diagram, there is an unstimulated receptor between, so the objects are seen as two distinct objects. The distance from the lens to the retina is about 16 mm. (a) What is the angular resolution of the eye due to the spacing of the photoreceptors in the fovea? (b) Under bright light conditions, the pupil is about 2.0 mm in diameter. What is the angular resolution of an eye for blue light (450 nm) for a pupil of this diameter? Assume n(eye) =1.3. (c) What is the resolution for blue light under dim light conditions where the pupil’s diameter is 6.0 mm? (d) Do bright light conditions lead to better resolution? Why or why not? (e) At what pupil size is the angular resolution due to diffraction less than that due to receptor spacing?

Figure P25.61 Resolution of two objects and receptor cell density.