Biomedical Engineering Reference
In-Depth Information
THE VERGENCE RELATIONSHIP
As with spherical refracting surfaces and lenses, the vergence relationship can be used
to locate the image produced by a mirror and to determine its magnification. We need
to keep in mind, however, that after reflection the direction of the light is reversed.
Consider this example.
An object is located 80.00 cm in front of a concave mir-
ror that has a radius of curvature of 33.33 cm. The object is 5.00 cm in height.
Where is the image located? Is the image real or virtual? Is it erect or inverted?
What is its height?
The solution to this problem is illustrated in Figure 14-7. Since the center of
curvature is located to the left of the mirror's surface, this distance is negative. The
power of the converging mirror is
−
2
r
F
=
−
2
=
F
−
0.3333 m
=
F
+
6.00 D
This makes sense because we know that all concave mirrors have positive power.
-80.00 D
-1.25 D
+6.00 D
O
F
′
C
I
+4.75 D
-21.05 cm
Figure 14-7.
Formation of a real, minified, and inverted image by a converging mirror.
The paraxial relationship can be used to determine the location and size of the image.
For this and following diagrams in this chapter, the object vergence and mirror power
are given at the top of the mirror and the image vergence is given below the mirror.
See the text for details.
