Mirror arrangements considered for the E-ELT Nasmyth configuration with mirrors and intermediate focus (IF) of the telescope marked. a) Straight-through configuration, with the Nasmyth focus directly after the fifth reflection. b) Lateral configuration, with a sixth mirror fixed in the Nasmyth port. The Q, U, V box represents a perfect full-Stokes polarimeter at the corresponding Nasmyth focus. The rotation axis of the telescope and the ± Q directions at the intermediate focus position are indicated. Adapted from Delabre (2008).