Book excerpt: This practical guide is a compendium of frequently asked questions (FAQs). The answers are provided in graphs, equations, or diagrams. An engineering approach is taken, the equations may be approximations, but the region of applicability is clearly stated. Facts, rules-of-thumb, and back-of-the-envelope equations are highlighted. This easy-to-read reference covers optical systems, detectors, cameras (visible and infrared), sampling effects, Moiré patterns, system performance, resolution, system testing, lasers and lidar, fiber optics, and data analysis.