NGC4559 is little bit forgotten intermediate spiral galaxy in Coma Berenices. It is located about 30 million light years away and belongs to Coma I Group of galaxies. Under dark sky can be spotted with medium sized binoculars, and in 100mm refractor it is obvious oval shape at low magnifications. Its apparent dimensions is 10×4 arc minutes, so it is pretty large (like one third of apparent Moon diameter), but to see the faint halo you need larger telescope.
I made image below in April, 2018 at my backyard observatory. It is LRGB composition, about 3 hours of total exposure with Meade ACF 10″ telescope and QHY163M camera on EQ6 mount. Transparency was good, seeing moderate.
There are quite a few HII regions in NGC4559, some of them have their own designations:
Image technical data: Date: 20.04.2018, 06.05.2018 Location: Nieborowice, Poland Telescope: Meade ACF 10" Corrector: AP CCDT67 Camera: QHY163M, gain 100 Mount: SW EQ6 Guiding: SW 80/400 + ASI290MM Exposure: L 50x2, RGB 15:10:12x2 minutes Conditions: seeing average-good, transparency good