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Optics - Focal length question

  • Thread starter Lux0r
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  • #1
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Homework Statement



For a lens with a focal length f, find the smallest distance possible between the object and its real image.

Homework Equations



1/s + 1/s' = 1/f

The Attempt at a Solution



I tried plugging in different numbers for the solution, but I'm not sure how to reach the solution..

The answer is s + s' = 4f
 

Answers and Replies

  • #2
ehild
Homework Helper
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What is the distance D between the object and image in terms of s and s'? Find the expression D(s). Differentiate D with respect to s and solve the equation D'(s)=0.
 

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