椭圆 $\frac{x^2}{a^2}+\frac{y^2}{b^2}=1(a>b>0)$的左、右顶点分别是 $A,B$,左、右焦点分别是 $F_1,F_2$.若 $\left|A{F}_1\right|,\left|F_1{F}_2\right|,\left|F_{1}B\right|$成等比数列，则此椭圆的离心率为.