New Digital Magnetograph at Big Bear Solar Observatory

A new magnetograph system has been installed and tested at Big Bear Solar Observatory. The system uses part of BBSO's existing VMG system: a quarter wave plate, a Ferro-Electric Liquid Crystal to switch polarizations, and a 0.25 Abandpass Zeiss filter tuned at CaI 6103 A. A 256 by 254 12-bit Dalsa camera is used as the detector and as the driver to switch the liquid crystal. The data rate of the camera is 90 frames/s. The camera is interfaced by a Pentium-166 with a Mutech imaging board for data acquisition and analyses. The computer has 128 MByte of RAM, up to 700 live images can be stored in the memory for a quick post-exposure image processing (image selection and alignment). We have improved the sensitivity and spatial resolution significantly over the old BBSO VMG system for the following reasons: (1) new digital image data is in 12 bits while the video signal is below 8 bits. Polarizations weaker than 1% can not be detected by a single pair subtraction in the video system. The d..