Question

What is the difference between first principal focus and second principal focus ???

Answer 1

Answer:

The first principal focus of a lens is the position of the object on the principal axis of the lens, for which the image is formed at infinity. ... The second principal focus of a lens is the position of the image on the principal axis of the lens, when the object is formed at infinity.

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Answer 2

Answer:

The difference between first and second principal focus of lens is that one Principal focus is front of the lens but second principal focus is back of the lens

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