This planetary nebula is known for the optical illusion it creates. Stare directly at it, and the nebula disappears; only the star at the center is visible. Look off to one side, the nebula reappears. The optical illusion occurs because the light falls on different cells in our retinas. Some are sensitive to light; the others are sensitive to color. 15" F/5 Dobsonian, 5mm LVW eyepiece (380x) + UHC filter. Mount Tamalpais State Park, CA. 2008-09-27.