Centroid position measurements and subpixel sensitivity variations with the MAMA detector

Initial measurements of the position sensitivity of a visible-light multi-anode microchannel array (MAMA) detector show that centroid calculations for image spots are accurate to better than 0.04 pixels even with sources that are essentially delta functions at the photocathode. Subpixel sensitivity variations of 10-15% are typically found for pixels in the array. Variations as large as 30% are possible in the worst conditions. These variations limit the photometric accuracy of the detector when very small scale features are observed. The photometric accuracy and the position sensitivity of the detector appear to be limited by cross-coupling effects within the anode array. Initial measurements with more recent designs of the detector show that most or all of this cross-coupling has been eliminated. We will report on the position sensitivity of the newer detectors when they become available for testing.