= Solution
For a partially filled $4f$ shell, the outer $5s$ and $5p$ shells shield the localized orbitals from the ligands. <Coulomb interactions> establish $L,S$ through <Hund's rules>, and <spin-orbit coupling> usually exceeds the much smaller <crystal field splitting>. First form a ground $J$ multiplet using $\mathbf J=\mathbf L+\mathbf S$, then split that multiplet by the crystal environment. The orbital contribution is therefore generally retained, and the <g-factor> is a multiplet Landé factor rather than an almost spin-only value. Weak external Zeeman and hyperfine interactions can subsequently resolve the remaining states. Exceptions with $J=0$ or unusual valence require separate treatment.
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