A person needs a lens of power, -5.5 dioptres for correcting his distant vision. For correcting his near vision, he needs a lens of power, +1.5 dioptres. What is the focal length of the lens required for correcting
- Distant vision, and
- Near vision?
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- For distant vision:
$\text{p}=\frac{1}{\text{f}}$
$\text{f}=\frac{1}{-5.5}=-0.1818\text{m}=18.18\text{cm}$
- For near vision:
$\text{1}=\frac{1}{\text{f}}$
$\text{f}=\frac{1}{\text{p}}=\frac{1}{1.5}$
$=0.6666$
$=0.66.66\text{cm}$
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