第四部分 典型光学系统

1. A person wants to look at the image of his or her own eyes, without accommodation, using a concave mirror of 60cm radius of curvature. How far must the mirror be from the eye if the person has 1) Normal vision?

2) 4diopter myopia, without correction? 3) 4diopter hyperopia, without correction? Solution.

1) When the person has normal vision, according to the following scheme 1, we get l'

so,

l

r

30cm2

2) According to the following scheme 2,

1

4m 1lr

l lr 25cm

112

l lr and l l 25(cm) r 60cm

Scheme 1

l2 85l 30 25 085 852 4 30 25l

2

85 65

2

l 75(cm) 1

l'1 50(cm), or l2 10(cm)

l'2 15(cm)

So the mirror must be 75cm or 10cm from the eye. 3) According to the following scheme 3,

Scheme 2

112 llr and l' l 25(cm) r 60cm

l2 35l 30 25 035 352 4 30 25l

2

35 65

2

Scheme 3

l 50(cm) 1

l'1 75(cm), or l2 15(cm)

l'2 10(cm) (Since the object is real, so we can give up this answer)

So the mirror must be 50cm from the eye.

2. Discussion: What differences between the following situations:

1) a microscope is used for projection; 2) the microscope is used for visual observation.