What is the 'front focal length' in optical terms?

The term 'front focal length' refers specifically to the distance from the front surface of a lens to its primary focal point. In optical terms, the primary focal point is where parallel rays of light entering from the front of the lens converge after passing through the lens. This concept is crucial in understanding how lenses focus light and is a fundamental principle in optics.

By correctly identifying the front focal length as the distance from the lens's front surface to the focal point, one can better comprehend how lenses interact with light and their role in optical devices. This is especially relevant for applications in eyewear, camera systems, and other visual aids, where precise focusing capabilities are essential for proper functionality.