Give the expression for the focal length of combination of lenses when.

i. Lenses are kept in contact with each other 

ii. Two lenses kept at a distance d apart from each other.

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1 Answers

i when lenses are kept in contact then

1/f = 1/f1 + 1/f2

f = f1f2 / f1 + f2

ii. When kept distant apart,

1/f = 1/f1 +1/f2 - d/f1f2

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