Hi
http://www.astrobin.com/full/268306/0/
The region around these galaxies has a very slight blue reflection nebulosity apparently due mainly to the bright star at the bottom of the field. It shows a similar pattern in my blue data and the blue DSS data, so is probably not an instrumentation artefact (see both heavily stretched blue images below).
Did not realise that there was a BOSS SN visible in IC4721 until I was recently processing the data.
https://www.flickr.com/photos/43846774@N02/26264696420. The now orange-red SN (Ha is beginning to dominate) is shown in the leftmost panel of the second image below, along with a previous image from my old 200mm scope, taken some time ago.
used the ASI1600 CMOS with 60 second subs, gain 100, for lum and RGB - but left my hard drive PS at the country site, so do not know exactly how many subs or when - from memory about 400, but will fill in Astrobin details when possible. Thanks for looking. Regards Ray