A dimmer for adjustably attenuating light to a fiber optic bundle. An opaque vane has a movement axis with a band on each side. One band has a substantially opaque portion which blocks about 50% of the light of a spot directed against the vane, and an opaque portion for passing about 50%. The other band has transmission slots interspaced between opaque bars, proportioned and arranged to pass varying amounts of light, all as a function of the position of the vane. The light passed by the bands is additive.