High accuracy, light-weight carbon fiber reinforced plastic (CFRP), membrane reflectors have been demonstrated by Composite Optics, Inc. (COI) for applications in ground based, millimeter wave radio astronomy. The surface figure of a semi- rigid membrane can be significantly improved by adjustment with an array of passive adjusters the support the membrane. A factor of ten contour improvement is possible. First, the surface is measured and analyzed for distortion from the desired shape. Then adjustment instructions are calculated by a customized software program and applied to the adjusters. This process is repeated to produce dimensionally stable reflectors, several meters in diameter at or below 25 micrometers RMS.