H-alpha (ionized gas) and H I kinematics for the HCG B/C/D group point to a giant, highly irregular galaxy with several knots, at least in the 2000 paper "Kinematics and morphology of ionized gas in Hickson Compact Group 18"
Through my 18", HCG 18A was very faint, but not too difficult with averted, perhaps 30"x20" NW-SE. The combined glow of connected HCG 18B, C and D was an extremely faint, elongated haze, though it was larger than HCG 18A just 1.5' SE. No resolution of the components B-C-D in this scope.
Through Jimi's 48", it was a different story, of course. HCG 18A appeared moderately bright and large, very elongated 7:2 WNW-ESE, ~40"x12", with a small brighter core.
HCG 18D is the northwest component of UGC 2140. It appeared as a fairly faint, very small knot, just 6"-8". This knot is embedded in a low surface brightness glow extending to the southeast that contains 18C and 18B.
HCG 18C is the central component. Its nucleus appeared faint, also very small, ~9"x6" and surrounded by low surface extensions to the northwest and southeast, merging into HCG 18B on the southeast end.
HCG 18B is fairly faint, very elongated 3:1 or 4:1 NNW-SSE, perhaps 45"x12". This portion of UGC 2140 is a similar in size to HCG 18A but with a fairly uniform surface brightness. A mag 15.5-16 star lies 0.6' E. I can see very faint haze bulging out just east of HCG 18B.
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