By using a cocycle generated by the step function φβ,γ=1[0,β]−1[0,β](.+γ) over an irrational rotation x→x+αmod1, we present examples which illustrate different aspects
of the general theory of cylinder maps. In particular, we construct non ergodic
cocycles with ergodic compact quotients, cocycles generating an extension
Tα,φ with a small centralizer. The constructions are related
to diophantine properties of α,β,γ