Find the focal length and nature of a lens whose optical power is -5D.

Explanation

To find the focal length and nature of a lens whose optical power is -5D, we can follow these steps:

### Step 1: Understand the relationship between power and focal length
The optical power (P) of a lens is related to its focal length (f) by the formula:
\[ P = \frac{1}{f} \]
where P is in diopters (D) and f is in meters (m).

### Step 2: Substitute the given power into the formula
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