Continuity mistake: When Yoda and R2-D2 are engaged in a tug-of-war over the little flashlight, Yoda hits him several times with his walking stick. When Artoo lets go, the stick is pointing upwards as Yoda hits him one last time, but in the next shot, Yoda is using it as a walking stick again and it is pointing downwards.
Revealing mistake: Look carefully at the end of the cavern where the Millenium Falcon enters the giant asteroid. It's a dark blue circle, because the light is dim. But there is a little white circle on the right and the two circles are much brighter on the left side. It's because it's an image of a planet with a moon.Dr Wilson
Revealing mistake: If you closely when Vader cuts through the three poles at the end of the lightsaber duel, you can see that the saber never actually goes through the poles. (01:45:50)
Revealing mistake: When we see the Star Destroyer for the first time, there are three of them on screen. The one on the top left, can still be seen even after another Star Destroyer came into frame and blocks the view.
Continuity mistake: Widescreen version: After Vader chokes Captain Needa, he talks to Admiral Piett. The distance between Piett and the officer next to him differs between shots, depending on the camera angle. (01:10:55)
Continuity mistake: After R2-D2 opens the door to the landing platform during the escape from Cloud City, the droid exits through the door. Some shots later, he is back inside. (01:43:55)
Continuity mistake: When Darth Vader and Admiral Piett are talking on board the Star Destroyer at the end of the movie, in the first shot, a man is standing behind Piett. In the next shot of Vader and Piett, a different man is standing behind Piett. Then, in the third shot of Vader and Piett, the first man is back. Widescreen version only.
Continuity mistake: When Vader is about to tell Luke that he is his father, as Luke says, "He told me enough," he is holding onto one of the thin poles next to him. In the next shot, his hand is positioned lower down and clutching the other pole. Also, his head is in a different position, seen from the markings on one of the other poles. The position of his head and hand changes in the next shot as well. (01:46:35)