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Question
Consider a point at the focal point of a convergent lens. Another convergent lens of short focal length is placed on the other side. What is the nature of the wavefronts emerging from the final image?
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Solution
Orientation of wavefront is perpendicular to ray. The ray diagram of the situation is shown in figure.
Parallel rays incident on lens L1 forms the image I2 at the focal point of the lens. This image acts as object for the lens L2 Now, due to the converging lens L2 , let final image formed is I which is point image. Hence the wavefront for this image will be of spherical symmetry.
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