We report on a mode-mismatched thermal lens experiment performed to quantitatively evaluate thermal and electronic laser-induced lensing effects in ion-doped crystals Cr3+:LiSAF, Yb3+:KYW, and Yb3+:YAG. The large diameter of the probe beam resulted in a slow thermal effect (∼dozens of milliseconds) two orders of magnitude larger than the electronic one, improving the discrimination of both competitive effects. All thermal and electronic parameters are obtained from transient signals modeled by an analytical equation, valid for small phase shifts in the absence of upconversion effects.