Rochester cloak

Rochester cloak is a type of cloaking device, which uses only 4 lenses. In the version presented in this simulation, the focal length of the two external lenses is \(f_1\), and of the two mid lenses is \(f_2\), such that the distance between consecutive lenses of focal lengths \(f_1\) and \(f_2\) equals \(t_1=f_1+f_2\), and the distance between the mid lenses is \(t_2=2f_2\frac{f1+f2}{f1-f2}\).