For mechanical engineers who design and analyze optical systems, this text outlines the theory and applications of optomechanical constraint equations, focusing on first-order, or Gaussian, optical imaging effects. It details the nature of optical imaging and the coordinate systems and sign conventions; the optomechanical influence functions; the optomechanical constraint equations that control the position, orientation, and size of the images of simple and complex optical systems; other optical elements that can be incorporated into the optomechanical constraint equations, such as the flat-fold mirror, powered mirror, window, diffraction grafting, and prism; computational methods; analysis performed using the equations; and their application to an optical image correlator, a fiber optic spread-spectrum encoder, and an infrared imager. Familiarity with the physics of optical imaging and additional experience in the optical industry are assumed. Annotation ©2016 Ringgold, Inc., Portland, OR (protoview.com)