λ1λ2=f1f2\frac{\lambda_{1}}{\lambda_{2}}=\frac{f_{1}}{f_{2}}λ2λ1=f2f1
λ1λ2=f2f1\frac{\lambda_{1}}{\lambda_{2}}=\frac{f_{2}}{f_{1}}λ2λ1=f1f2
λ1λ2=f1f2\lambda_{1} \lambda_{2}=f_{1} f_{2}λ1λ2=f1f2
λ1λ2=f1f2\frac{\lambda_{1}}{\lambda_{2}}=f_{1} f_{2}λ2λ1=f1f2