A variable optical filter is disclosed including a bandpass filter and a blocking filter. In the display device, light-path converting members are provided on stationary members to change a path of a light inputted obliquely through stationary members and movable members vertically with respect to a display screen. The lowest center point of the triangle shape allows the handles carried to settle at a central, low point, for a secure and balanced load carrying ability. Cooling of the retractor allows the retractor to maintain the expanded characteristic. The monopole tower may be positioned with the vertically extending outer corner aligned with the land-based radar site so that the pair of adjacent vertical facets reflects radar illumination away from the radar site to reduce an amount of the radar illumination reflected back to the land-based radar site. The memory stores an image defect visibility predictor that, when executed by the processor, compares an original image with a defect image and outputs a predicted defect visibility image that accounts for defect masking by the original image.