Understanding camera lens focal length and magnification

1. Camera lens focal length

  - Focal length means the distance from the lens to the image sensor

- The focal length of a compound lens, composed of a series of simple lenses, is the distance from the

  second focal point to the image sensor

2. Focal length and magnification

  - The lens magnification is determined as the ratio between the minimum and maximum

    focal lengths

    Eg.) 20-100mm For zoom lenses with variable focal lengths, it is expressed as "5x optical zoom