Page 50 - Modern Optical Engineering The Design of Optical Systems

Gaussian Optics: The Cardinal Points 33

Note that a more exact value for the image thickness and the longitudinal
magnification can be obtained by calculating s′ for two object distances, 1 in
apart. If we use object distances of 20 in and 21 in, we get an image distance
difference (image thickness) of 0.038462 in. Using 19 in and 20 in, we get
0.041667 in. Using 19.5 in and 20.5 ft, the result is an image thickness of
0.040016 in.

4 The first principal point of a 2 in focal length lens is 1 in from the object.
Where is the image, and what is the magnification?
ANSWER: Using Eq. 2.5, we find the image at
s′ s f/(s f )
s′ 1 2/( 1 2) 2/1 2 in
The image is 2 in to the left of the lens, and the magnification m s′/s
2/( 1) 2 .