Funny how hindsight changes things. As the comet faded off in Jan-Feb-Mar, it took heavier & heavier processing to reveal anything. Now, looking back, there's a lot more to be got from the shots when the comet was bright.
This one for instance, from 26 Dec 2011 (morning of 27 Dec our time). At the time, my report was that this shot showed 33 deg of tail and that 26 deg was visible visually. With a bit more juice, 38 deg is clearly showing in the shot. Not only that, "greater than 38-deg" would be a better estimate because the tail gets cut off pretty abruptly by vignetting on the edge of the top frame.
http://i727.photobucket.com/albums/w...dec2011inv.jpg
Here's the 'normal' version of the 4-frame stitch, each 3 x 2 min with Canon 400D at 55mm (incidentally, just got around to stitching these!). Note the band of green airglow above the horizon:
http://i727.photobucket.com/albums/w...11lgecrasm.jpg
And here's a mangled positive version:
http://i727.photobucket.com/albums/w...ec2011deep.jpg
Cheers -