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Unformatted text preview: cus, do the red and blue
colors (wavelengths) come to exactly the same focus? (You can use color ﬁlters to better separate colors,
Record the focal point distances and measure the radii of the lens surfaces by carefully tracing the lens
shape (see Figure 6 for the necessary measurements).
Calculate the expected focal length using the Lens Maker’s Equation (Equation 5) found in Section
2.5. Compare it to your measured focal length. (Note that for lenses with one straight surface, 1/R is zero
for that particular surface!)
Finally, consider the smearing (i.e., aberrations) in the focal lengths you noted above for rays in different positions and of different colors. These problems are the result of the lens being a non-ideal shape
(circular rather than parabolic) and the fact that n, as we’ve noted, is actually a slight function of λ . These
two effects result in spherical aberration and chromatic aberration respectively. 7 Ray Box Rays set parallel
Figure 5: Single lens setup. R R-d ( ) 1 —2
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This document was uploaded on 02/15/2014.
- Spring '14