Camera lens

Electricity and Magnetism Level 3

The lens in your digital camera has a diameter of $$2.5 \text{ mm,}$$ and according to the manufacturers' specifications, its f-number is $$“ \text{F} 4.0 ”.$$ The lens is held a certain distance away from the detector in order to produce a well-focused picture of a flower that is $$15 \text{ cm}$$ away. You then turn to take a picture of a distant landscape. How far must the lens be moved, and in which direction, in order to obtain a well focused picture of the landscape?

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