Achromatic combination

\(\therefore \theta_{\text {net }}=0\)

\(\theta_{1}-\theta_{2}=0\)

\(\theta_{1}=\theta_{2}\)

\(\omega_{1} \delta_{1}=\omega_{2} \delta_{2}\)

\(\&\, \delta_{\text {net }}=\delta_{1}-\delta_{2}=2^{\circ}\)

\(\delta_{1}-\frac{\omega_{1} \delta_{1}}{\omega_{2}}=2^{\circ}\)

\(\delta_{1}\left(1-\frac{\omega_{1}}{\omega_{2}}\right)=2^{\circ}\)

\(\delta_{1}\left(1-\frac{2}{3}\right)=2^{\circ}\)

\(\delta_{1}=6^{\circ}\)

\(\delta_{1}=\left(\mu_{1}-1\right) A_{1}\)

\(6^{\circ}=(1.5-1) A_{1}\)

\(A_{1}=12^{\circ}\)