Chapter 2 Chapter 2 Question 1 a-f, page 42. And there should be nicer parenthesis and such. Question 2, p. 42. A six diopter lens must be placed in the light path to compensate for the defocus in the optical path. The horizontal and vertical dimensions cannot be brought into focus simultaneously.
Chromatic aberration is mainly due to the water in the eye, which is the same from person to person.
The 6-diopter correction will have a wider linespread function. The contrast at higher spatial frequencies will be lower for the 6-diopter case than the 3 diopter case. They needed a point source, not just a line source. This would have emitted fewer quanta and thus had additional signal to noise measurement problems. A line is the sum of points.