Page 324 - Modern Optical Engineering The Design of Optical Systems

Optical System Layout 303

Figure 13.10 The sum of the
element power as a function of
the choice of the objective focal
length.

material which is contained in subsequent chapters. In general, how-
ever, a minimum | | in this example would reduce the Petzval cur-
vature of field, a minimum |D | would reduce the cost of making
the optics, and minimum |D |, |y |, or |y | would tend to
2
reduce other aberrations, the choice being dependent upon which
aberration one most desired to reduce.
Assuming that we have chosen f o 4, the values of the lens powers
and spacings would be determined as follows:

f 4
o
4 4 4 10 4 (4 4 4 10)
f 1.8298
e
4 4 (4 10) 4 (4 1) (4 1)
4 (10 4 1.8298)
s 1.4737
1
(4 1.8298 4)
( 1.4737) 4 1.8298
s 2.6965
2
4
( 1.4737) 4 1.8298
f 0.9529
r
(4 1.8298 4)

13.4 The Simple Microscope or Magnifier
A microscope is an optical system which presents to the eye an
enlarged image of a near object. The image is enlarged in the sense
that it subtends (from the eye) a greater angle than the object does
when viewed at normal viewing distance. The “normal viewing distance”
is conventionally considered to be about 10 in; this represents an average
value for the distance at which most people see detail most clearly.