An instrument designer discusses the design, use, and limitations for optics based failure analysis tools for circuits. We will discuss conventional microscopes in the FA lab as well as emission microscopes, laser-based microscopes (e.g: OBIRCH, XIVA), and infrared microscopes. We will also cover the “pain and gain” of employing HgCdTe and InGaAs detectors for emission microscopes. Infrared techniques for locating shorts from the back side including OBIC, OBIRCH, LIVA, TIVA, and XIVA laser techniques and locating faults with thermal infrared techniques will be described.