Production costs for a full-frame sensor can exceed twenty times the costs for an APS-C sensor. Only 20 full-frame sensors will fit on an silicon wafer, and yield is comparatively low because the sensor's large area makes it very vulnerable to contaminants—20 evenly distributed defects could theoretically ruin an entire wafer. Additionally, when full-frame sensors were first produced, they required three separate exposures during the photolithography stage, tripling the number of masks and exposure processes. Modern photolithography equipment now allows single-pass exposures for full-frame sensors, but other size-related production constraints remain much the same.