# Magnetic lens

The passing particle is subjected to two vector forces $H_Z$ (parallel to the core), and $H_R$ (parallel to the radius of the lens). $H_Z$ causes the particle to spiral through the lens, and this spiraling expose the electron to $H_R$ which in turn focus the electron. Note that the magnetic field is inhomogeneous, particles close to the center are less strongly deflected than those passing the lens far from the axis.[1]