Lens Formula and Sign Convention
The lens formula is a fundamental equation in optics that describes the relationship between the focal length (f), the image distance (v), and the object distance (u) for lenses. It can be expressed as:
\[ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \]
In this equation:
- Focal Length (f): The distance from the focal point to the optical center of the lens.
- Image Distance (v): The distance from the optical center to the image formed by the lens.
- Object Distance (u): The distance from the optical center to the object placed before the lens.
The sign convention used in this context is the Cartesian sign convention. Under this convention, distances measured against the direction of the incident light are taken as negative, while distances measured in the direction of the incident light are positive. Understanding and applying this sign convention is crucial when working with the lens formula, as it determines whether images are classified as real or virtual, inverted or erect.