A person uses a lens of power -2.0D for correcting his distant vision. For correcting his near vision he uses a lens of power +1.5D. What is the focal length of the lenses required to correct this disorder ?

$f=\frac{1}{Power}$

On substituting the given values for both the lenses we get,

${f}_{concave}=\frac{1}{-2.0D}=-0.5m=-50cm\phantom{\rule{0ex}{0ex}}and\phantom{\rule{0ex}{0ex}}{f}_{convex}=\frac{1}{1.5D}=0.67m=67cm$

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