Star Wars: Episode V - The Empire Strikes Back (1980)

Revealing mistake: Right after Luke and Darth fight for the first time, Darth gets kicked off of the Carbonite freezer. Then Luke jumps down to fight him again. After he jumps, you hear what sounds suspiciously like a trampoline. Then in the lower right screen you can see Mark Hamill's head pop back up into frame. Widescreen only, although the sound is audible on the 4:3 version too.

Revealing mistake: During the battle on Hoth, after Luke says: "Hobbie, you're still with me?", there's a shot of an AT-ST shooting at the rebel and after that, there a shot of an explosion behind them. You can see that the rebels are actually dummies in that shot.

Revealing mistake: When Luke quits Hoth, the planet is actually painted on a glass sheet but the problem is that you can see a line joining two sheets.

Revealing mistake: When Yoda is training Luke by having him do a handstand and stack some rocks, watch closely during the close-up of one of the rocks. You can see a string holding it in the air. (01:08:30)

Revealing mistake: When the Millennium Falcon is being pursued by the Star Destroyers after leaving Hoth, for a few seconds you can see the light of the ship through one of the Star Destroyers as the Falcon flies in front of it in the second shot. (00:35:25)

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.

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.

Revealing mistake: If you look closely when Vader cuts off Luke's hand, you can see that Vader's lightsaber never actually cuts through Luke's wrist, but passes in front of his hand. (01:45:55)

Revealing mistake: When Luke runs into Vader again after being sucked out the window, as they are fighting in the control room, watch closely: Vader's lightsaber hits the wall a couple of times, but the explosions are not where the saber touches the wall. (01:45:20)

Revealing mistake: When the Millenium Falcon fakes hitting the Star Destroyer, half of the sky is gray and the other half is black.

Revealing mistake: Before Lando warns the people of Cloud City that the Empire has taken control of the city, Leia shoots a stormtrooper. The burn mark can be seen on the troopers armour before the laser beam hits him. (01:42:40)

Revealing mistake: After Luke escapes from the snow monster, he collapses, and there's a shot of Han riding. When the camera pans down, there are no tracks in the snow where the tauntaun just ran. (00:11:00)

Revealing mistake: When the stormtroopers are firing at Chewie and the droids and C3PO is yelling at R2D2 about the Millennium Falcon's hyper-drive, there is a shot of Chewie being shot at and the beam putting a hole in the wall. In one shot, it doesn't look much bigger than a pinpoint, but in the next shot, the team at Industrial Lights and Magic were kind enough to add a CGI burn mark, which contracts, almost disappears, and then warps as smoke passes in front of it, wrecking the illusion.