# Rochester cloak

Contributor: Stas Fainer

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 $$t_2=2f_2\frac{f1+f2}{f1-f2}$$.