15.9 Resolving Power of the Eye

15.9 Resolving Power of the Eye

• The resolution goes down, but the sensitivity to light and movement goes up.

• We can see an object only about 4 cm in diameter from a distance of about 2 m. An image about the size of the fovea is projected into an object of this size.

• The objects are seen clearly but not with complete sharpness.
• The central part of large objects is less distinct.

• For example, if we focus on a person's face 2 m away, we can see clearly the facial details, but we can't pick out a subsection about the size of the mouth.
• We can see the person's arms and legs, but we can't see details about their shoes.

• In our discussion of image formation so far, we have used geometric optics, which neglects the light's diffraction.
• Light from a point source is assumed to be focused into a point image.
• This isn't the case.

• It is not possible to distinguish the two points of a light source that is close together.
• An optical system can resolve two points.

• Experiments show that the eye doesn't work well.
• Most people can't resolve two points with a small separation.
• There are other factors that limit the resolution of the eye.
• There are problems with the lens system of the eye.
• The structure of the eye is important.

• To resolve two points, the light from each point must be focused on a different cone and the excited cones must be separated from each other by at least one cone that is not excited.

• The lens should be considered as the focal point of the optical path.