1.From user requirements to system specifications
1.Objectives for the optical system
2.Optical technologies and how they can meet performances.
3.Typical numerical values (or ranges) for the most important parameters  (resolution, field of view, temporal issues, … ).
2.Architecture
1.Physical principles of the measurement.
2.Subsystems, functions and interfaces
3.Overall geometry: “universe” and  system / instrument reference systems.
4.Sampling issues and identification of the factors determining resolution
5.Most relevant sources of noise and noise reduction approaches.
6.Subsystems constraining performances.
3.Markets
1.Examples of an actual instruments and/or technologies available

Signal and data processing are outside the scope of the essay, unless they play a role in defining engineering parameters (such as resolution) or are necessary to compensate hardware under-performances.