M51 exposure times are LUM=39 5min. plus R,G,B=10,10,10 5min. subs. taken with a telescope focal lenght~2m., Optec NextGEN Wide Field 0.5X reducer used. Due to light polution from the city of Copenhagen additionally a IDAS LPS filter was used. CCDStack and Adobe Photoshop CS4 applied for picture processing. Dark, flat and bias frames used for calibration of the raw LRGB frames. Picture size is 66% of the original size.
Picture published in S&T archive:http://media.skyandtelescope.com/images/M51_MASTER_LRGB-IP-SSHR-66-MIX-crop.jpg