First time with colour filters

Up until last night, I have only used narrow band filters with my ZWO asi1600mm Pro Monochrome camera, mainly because during the winter months the majority of imaging is of nebulous objects, with the milkyway high overhead there is a vast number of these deep sky targets to choose from – now that the long nights are over, it’s the turn of the galaxies to occupy the imagers time. However narrow band imaging shows little on these distant islands of stars, only Ha really picks out the star forming regions and then only on the closer galaxies, this means that galaxy imaging is done with wideband filters, Red, Green and Blue, I decided to image M51 the Whirlpool galaxy in the constellation of Canes Venatici, below the handle of the Big Dipper, changing from my narrow band filter wheel to my colour filter wheel only took a few minutes, however the focus position was way off – luckily it was outward focus travel that was required as my narrow band filter focus position leaves me with only 2.5mm of inward focuser travel remaining. I managed 45 x 300 second exposures giving me 3.75 hours worth of data with the red filter. I now need to do the same with the green and blue filters and combine the three mono images in Photoshop to create a colour image, I will then use the Ha filter for the star forming regions and add this data to the image followed by a luminance for detail. The forecast looks good again for tonight, when I’ll use the green filter – this is the only disadvantage to using a  mono camara, you have to use multiple filters to create a colour image but the result is far better than using a colour camera alone.

M51 Red filter
M51 Red filter

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