William Herschel discovered NGC 2604 = H III-292 = h509 on 12 Mar 1785 (sweep 385) and recorded "vF, pL, R, lbM, resolvable. 2 or 3 pB stars about it." His position is ~10 sec of RA too far east and 2' too far south. John Herschel logged it on 27 Jan 1827 (sweep 56) as "eF; doubtful obs, as at first the neb was hardly seen. Verified, but too late for a good RA. In field with a double star which points rather s of it." The 10 Dec 1866 observation by Robert Ball with LdR's 72" reads "eF, vL, center not uniformly bright, but the luminous portion lE and curved, convex preceding (this was little more than a suspicion); vF double star close north."

400/500mm - 17.5" (3/28/92): faint, moderately large, 2.0' diameter, low even surface brightness, slightly elongated but irregular or ill-defined outline. A mag 14 star is 1' off the south edge and 1.8' from center. A very faint close mag 15/15.5 double is at or just off the WNW edge. Almost collinear with a double star 5' SSE with components mag 10/10.5 at 32".

600/800mm - 24" (4/28/14): fairly faint, fairly large, round, 1.6' diameter, broad weak concentration but there was no core or zones. The halo gradually fades out. A pair of faint mag 15.5 stars at ~20" separation lies 1.3' NW (outside the halo). A bright 30" pair of mag 10.3/10.8 stars lies 5' SSE. Forms a pair (probably interacting) with CGCG 149-049 = NGC 2604B 3.6' SE. The companion appeared extremely faint, very small, elongated 2:1 SW-NE, 20"x10" and required averted vision at 260x.

Notes by Steve Gottlieb