Simply put, vary focal lens is a lens that can zoom in and out. You can adjust the lens so that it captures a wider area or so that it focuses in more detail on a smaller area. ... Generally, the smallest aperture size of vary focal lenses used in home security cameras is 2.8-12mm, and the largest is 5-100mm. We can vary the Lens by manual or Motorized. These cameras allows up to 120m from 20m IR effective distance.