The measure of oneâs ability to perceive spatial differencesbetween objects is termed visual acuity. For this problem, assumethe center-to-center cone spacing in the human fovea is 2.5 µm, andthat the focal length of the eye is 24.3 mm (the distance from thefront of the eye to the retina).
(a) If the criterion for the eye to distinguish between two pointobjects in space is that there must be one unstimulated cone lyingbetween the two cones stimulated by the light from the pointobjects, what is the acuity of the eye in arc-minutes?
(b) Measurements have shown that an emmetropic eye has about 1arc-min of visual
acuity. Does this agree with the result you computed in part (a)?If not, give some
reasons why this might be.
(c) Imagine that you are designing a freeway traffic sign. Theletters should be clearly
readable by a person with normal vision from a quarter-mile away.What is the
smallest linewidth that the letters can have?
(d) During a long drive to Las Vegas, Patrick is sitting in thefront passenger seat, trying to read the reversed numbers on thefront license plate of the car behind him by viewing them throughthe passenger-side rear-view mirror, which reads, âObjects in themirror are closer than they appear.â Patrick is famous for hisknowledge of trivial facts, so he happens to know that a commonfocal length for these mirrors is 1350 mm in magnitude and that thelinewidth of the numbers on a license plate is 9 mm. If the car isapproaching from behind and one lane to the right, at what distancecan he start to clearly read the numbers on the license plate?
The measure of oneâs ability to perceive spatial differencesbetween objects is termed visual acuity. For this problem, assumethe center-to-center cone spacing in the human fovea is 2.5 µm, andthat the focal length of the eye is 24.3 mm (the distance from thefront of the eye to the retina).
(a) If the criterion for the eye to distinguish between two pointobjects in space is that there must be one unstimulated cone lyingbetween the two cones stimulated by the light from the pointobjects, what is the acuity of the eye in arc-minutes?
(b) Measurements have shown that an emmetropic eye has about 1arc-min of visual
acuity. Does this agree with the result you computed in part (a)?If not, give some
reasons why this might be.
(c) Imagine that you are designing a freeway traffic sign. Theletters should be clearly
readable by a person with normal vision from a quarter-mile away.What is the
smallest linewidth that the letters can have?
(d) During a long drive to Las Vegas, Patrick is sitting in thefront passenger seat, trying to read the reversed numbers on thefront license plate of the car behind him by viewing them throughthe passenger-side rear-view mirror, which reads, âObjects in themirror are closer than they appear.â Patrick is famous for hisknowledge of trivial facts, so he happens to know that a commonfocal length for these mirrors is 1350 mm in magnitude and that thelinewidth of the numbers on a license plate is 9 mm. If the car isapproaching from behind and one lane to the right, at what distancecan he start to clearly read the numbers on the license plate?
