Biomedical Engineering Reference
In-Depth Information
The negative image vergence confirms that the image is virtual. It is formed by
diverging rays that exist in air, and its distance is calculated as follows:
n
′
′
=
L
′
l
or
n
L
l
′
=
′
1.00
3.50 D
′ =
l
0.2857 m, or 28.57 cm
Since this virtual image is located 28.57 cm below the surface, the quarter
appears
closer to the surface than it really is. The lateral magnification is
L
L
l
′ =
M
L
=
′
−
3.50 D
M
L
=
−
3.50 D
M
L
= +
1.00
×
The
image
of the quarter is of the same size and orientation as a quarter itself.
8
The alternative solution to this problem, in which we use linear sign conventions,
is illustrated in Figure 3-9. The aquarium is tilted so that it stands on its side. Now,
we can assume that light travels from left to right. The only tricky thing is to keep
straight which indices should be used to calculate object and image vergences. Since
the object “lives” in water, the object vergence is
n
l
L
=
1.33
L
=
−
0.38 m
3.50 D
As is the case for other surfaces we discussed in this chapter, the object vergence
in Figure 3-9 is given above the surface, as is the surface power of zero. The image
vergence, which is given below the surface, is determined with the vergence rela-
tionship as follows:
L
L
= −
′
=
L
+
F
L
′ = −
3.50 D
+
0.00 D
L
′ = −
3.50 D
8. Although the image of the quarter is the same size as the quarter, it appears larger because it is
closer to the surface. This is referred to as angular magnification (discussed in Chapter 12).
