“examining Osterberg’s data shown above it can be seen that rod receptors begin to “intrude” into the all-cone foveal region at very small retinal angles. It is not really obvious in the figure how small an angle this is but a statement from Pirenne (Vision and the Eye, The Pilot Press Limited, London, 1948) gives the magnitude…..”The first rod…..is situated at distance of 0.13 mm from the foveal center”.

I completely understand..and have noted…that cone size differs from person to person..and varies across the retina.The widely spaced, and very few, cones of the peripheral retina are smaller in diamater than foveal cones. I have said that I do not know the function of these cones but speculate that they evolved to detect a portion of the primary Fourier transform of the long wavelength sensitive fovea….a small fraction of this FT should be seen at these large angles. Further, I can predict that the response of these light detection centers should be on the green side of mid-band following from the smaller cone-rod appostion.

I have noted that cone-cone separation may/should vary between individuals/populations, genetically mediated, following from some evolutionary advantage in seeing at longer wavelengths (better night vision?). I have stressed rod size defferences as this apposition mediates the short wavlength, potentially bioiogically damaging, UV limit of visual response. Both of these premises should be testable in different populations.

I really wish that you might step back and examine the basic premise here…that the historically measured distribution of rods and cones on the retinal surface is in exact consonance with light diffraction within the eye and (absolutely!) leads to the conclusion that the eye is a Fourier tranforming device.

Two facts about cone size - it varies from person to person, and, varies across the retina.