Physics - Geometrical Optics Question with Solution | TestHub

For achromatic combination

$\frac{\text{f}}{{\text{f}}^{\prime }}=-\frac{\text{ω}}{{\text{ω}}^{\prime }}$

but$\frac{\text{ω}}{{\text{ω}}^{\prime }}=\frac{{\text{ω}}_0}{2{\text{ω}}_0}=\frac{1}{2}$

$-\frac{\text{f}}{{\text{f}}^{\prime }}=\frac{1}{2}\text{or}{\text{f}}^{\prime }=-2\text{f}$