An assembly, in particular an underwater optical assembly is provided. The assembly comprises a tubular wall mount, a housing and a seal. The wall mount has a cylindrical bore portion and the housing comprises a head and a stem rearwardly protruding from the head along an axis. The head defines a chamber with a window for dry housing an optical device in the chamber and the stem comprising an enclosed channel in fluid communication with the chamber. The stem has a cylindrical stem portion mated to the bore portion. The assembly is configured such that in an assembled configuration the stem portion fits the bore portion in an axial direction, the head is located in front of at least the bore portion of the wall mount, the housing being attached to the wall mount and plugging the wall mount with the seal extending substantially radially between the stem portion and the bore portion sealing the assembly circumferentially watertight. The head has a radial head size and the stem has a radial stem size, wherein the head size is larger than the stem size. The head has one or more circumferential walls forwardly protruding from a substantially radial rear wall, the stem rearwardly protruding from the rear wall. The stem and the one or more circumferential walls each have a thickness in radial direction, defining a rear wall area between a radial outside of the stem and a radial inside of the one or more circumferential walls, wherein the rear wall has, for at least half the radial area a thickness in axial direction that is less than a thickness in radial direction of the circumferential wall, and preferably less than a thickness in radial direction of the stem.