A non-circular, mechanically variable optical attenuator using a pair of specially constructed polarizing elements with means enabling a gradual transition from un-crossed polarization vector fields to crossed polarization vector fields using a linear motion with respect to one another. The polarizing elements whose polarization axis varies with spatial position on the element have a polarization vector field that is a function of position on the element. Specifically, the two polarizing elements have a defined orientation of polarization axes or vectors on the polarization vector fields that vary with spatial location on the polarizing element such that when aligned light passes, and when the polarization axes are crossed, light is attenuated. The present attenuator has a practical application for dimmable mirrors or windows by providing a variable optical attenuator that is purely mechanical and non-circular in shape. Dimming of the mirror or window is controlled by gradually sliding one such special polarizer with respect to the other.