The focal length of a lens depends on

We know lens maker’s formula

$\frac{1}{\mathrm{f}}=\left(\frac{{\mu }_{\text{lens }}}{{\mu }_{\text{sumoundingmedium }}}-1\right)\left(\frac{1}{{\mathrm{R}}_1}-\frac{1}{{\mathrm{R}}_2}\right)$

From this formula we can claim that focal length depends on

(i) radii of curvatures

(ii) refractive index of material used in lens

(iii) refractive index of surrounding medium