Neewer® 18mm rubber eyecup eyepiece Eyecup for Canon 550D 300D 350D 400D 60D 600D 500D 450D 1000D 400D D30 D60 (Electronics)
... That the eye cup slightly falls from the frame's true. Here helps a little superglue and the problem is solved (for a star deduction). Otherwise, the part is seated firmly on the eyepiece, so it's good that there is something seriously goes up.
