  We consider the composition of operators with non-closed range in Hilbert
spaces and how the nature of ill-posedness is affected by their composition.
Specifically, we study the \mbox{Hausdorff-,} Ces\`{a}ro-, integration
operator, and their adjoints, as well as some combinations of those. For the
composition of the Hausdorff- and the Ces\`{a}ro-operator, we give estimates of
the decay of the corresponding singular values. As a curiosity, this provides
also an example of two practically relevant non-compact operators, for which
their composition is compact. Furthermore, we characterize those operators for
which a composition with a non-compact operator gives a compact one.
