1. From http://www.rane.com/par-c.html: See also dynamic. 2. An optical system used in some profile spotlights, followspots, and projectors that consists of a spherical (usually) reflector, and a condenser lens as well as an objective lens. Fixtures using condenser optics are often able to project a sharper image than an equivalent ERS, but are often not as bright, due to losses in the optical path.