METIS: System engineering and optical design of the mid-infrared E-ELT instrument by Lenzen, R, Brandl, B, Pantin, E, Glasse, A, Blommaert, J, Venema, L, Ter Horst, R, Oudenhuysen, A, Molster, F, Siebenmorgen, R, Böhnhardt, H, Van Dishoeck, E, Van Der Werf, P, Brandner, W, Henning, T, Hippler, S, Lagage, P, Moore, T, Baes, M, Waelkens, C, Wright, C, Käufl, H, Kendrew, S, Stuik, R, Jolissaint, L