In this paper, we present two innovative optical systems dedicated to deep sea observation. The instrumentation and associated methodology are developed in the context of European project EXOCET/D (FP6-GOCE-CT-2003-505342, http://w3.ifremer.fr/exocetd) [SAR04]. The general objective of the project focuses on the design, the implementation and the test of specific instruments to explore, study and quantify biodiversity in the deep sea. The relationship between habitats and environmental dynamics is also an important issue of the project. The presented development takes benefit of work carried out at Ifremer for several years in the field of underwater imaging and measurement [CAD04].One specific target is to set up a complete methodology to make a 3D reconstruction of small scale scenes using stereovision techniques. To meet this scientific requirement, a new system, called IRIS (Invariant 3D Reconstruction by Instrumented Stereovision), has been specified and is under development. It includes the design of a stereovision head and the associated methods for data processing.For an operational use in an underwater environment, the stereovision head will be operated by Ifremers deep scientific Remotely Operated Vehicle victor 6000. The ROV is landed on the seafloor to keep a fixed and stable attitude, a small region of interest (around 1m3) is investigated by the stereovision rig mounted at the tip of victor 6000s instrumented robotic arm MAESTRO.