feq1=fL2−fm1fm=−2∣R2∣fL1=(μ1μ2−1)(R11+R21) $\begin{aligned}
& \frac{1}{\mathrm{f}_{\mathrm{eq}}}=2\left(\frac{\mu_2-\mu_1}{\mu_1}\right)\left(\frac{\mathrm{R}_1+\mathrm{R}_2}{\mathrm{R}_1 \mathrm{R}_2}\right)+\frac{2}{\mathrm{R}_2} \
& =\frac{2}{\mathrm{R}_2}\left[\frac{\left(\mu_2-\mu_1\right)\left(\mathrm{R}_1+\mathrm{R}_2\right)+\mu_1 \mathrm{R}_1}{\mu_1 \mathrm{R}_1}\right] \
& =\frac{2}{\mathrm{R}_2}\left[\frac{\mu_2 \mathrm{R}_1+\mu_2 \mathrm{R}_2-\mu_1 \mathrm{R}_1-\mu_1 \mathrm{R}_2+\mu_1 \mathrm{R}_1}{\mu_1 \mathrm{R}1}\right] \
& \frac{1}{\mathrm{f}{\mathrm{eq}}}=\frac{2\left[\mu_2 \mathrm{R}_1+\mu_2 \mathrm{R}_2-\mu_1 \mathrm{R}_2\right]}{\mu_1 \mathrm{R}_1 \mathrm{R}_2}
\end{aligned}Forsamesizeofimage\begin{aligned}
& \mathrm{u}=2 \mathrm{f} \
& \mathrm{u}=\frac{\mu_1 \mathrm{R}_1 \mathrm{R}_2}{\mu_2 \mathrm{R}_1+\mu_2 \mathrm{R}_2-\mu_1 \mathrm{R}_2}
\end{aligned}$