SPATIAL-FREQUENCY RESPONSE OF A PHOTORECEPTOR AND ITS WAVELENGTH DEPENDENCE .2. PARTIALLY COHERENT SOURCES

The response of an isolated model foveal cone to a partially coherent sinusoidal intensity source is explored with the methods of photorecep tor optics. This extends the work with coherent sinusoidal intensity s ources reported in part one [J. Opt. Sec. Am. A 11, 1193 (1994)]. The dielectric waveguide model of a foveal cone previously used to discuss the origin of the Stiles-Crawford effect and its wavelength dependenc e is applied to photoreceptor excitation by a partially coherent sinus oidal intensity source with variable spatial frequency and light wavel ength. The results indicate that the photoreceptors themselves contrib ute to visual acuity through a wavelength-dependent response at each s patial frequency and that the response is dependent on the spatial coh erence of the source. In particular the isolated photoreceptor has a c haracteristic low-pass-spatial-frequency filter effect for wavelengths between 410 nm and 654 nm (where two waveguide modes are carried). Th e coherent and the incoherent response curves are separated by differi ng amounts depending on the wavelength of the light. For wavelengths g reater than 654 nm (the single-mode region) the incoherent curve also has the shape of a characteristic low-pass-spatial-frequency filter, w hile the coherent curve shows a flat response. The results are used to discuss human eye modulation-transfer-function measurements. (C) 1997 Optical Society of America.