In 1966, George Abell produced a catalog of 86 objects that were believed to be planetary nebulae. Four of these were already listed in the NGC/IC catalogs, (Abell 50 is NGC 6742, Abell 75 is NGC 7076, Abell 37 is IC 972, and Abell 81 is IC 1454), and another 7 were later found not to be planetaries. (Abell 9, Abell 11 (reflection nebula), Abell 17 (red plate flaw), Abell 32 (red plate flaw), Abell 64, Abell 76 (ring galaxy PGC 85185), and Abell 85 (supernova remnant CTB 1).
The remaining 75 objects present some excellent challenges for the observer, both visual and imaging as most of the objects are very large and faint. Most times a large aperture is required and for visual observing, an OIII filter.