This invention concerns improvements relating to a deformable-mirror holder for holding a mirror in a desired position, to within accepted tolerances, even whilst the mirror is deforming or in a deformed state. More particularly but not exclusively, this invention relates to a holder for a bimorph mirror. A deformable mirror holder (31) is provided comprising a body with a receiving portion for receiving a deformable mirror (30), and wherein the receiving portion is defined by a passive flexible support structure (41) such that, in use, to the support structure provides a supporting surface to the mirror. This invention extends to a deformable mirror and a deformable mirror holder as described above.