@ARTICLE{Mueller:2008:ERing,
    author = {T. M{\"u}ller},
    title = {{Einstein rings as a tool for estimating distances and the mass of a Schwarzschild black hole}},
    journal = {Phys. Rev. D.},
    year = {2008},
    volume = {77},
    pages = {124042},
    pacs = {04.20.-q, 04.20.Jb, 04.20.Fy},
    doi = {10.1103/PhysRevD.77.124042}
}