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. But this good transparency was not enough to capture some extraordinary detail on NGC4559 galaxy, because 100 minutes of luminance is far too small amount of data. Especially under suburban light polluted sky. Imaging targets with faint regions (like galaxies or reflective/dark nebulae) is very tricky with light pollution present. Only extraordinary transparency of atmosphere may help. Narrowband imaging is little bit more forgiving.
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