Dr. Cyclops (1940)

Albert Dekker stars in this classic mad scientist movie as the short-sighted Dr Thorkel, who summons four scientists to his lair deep in the Peruvian jungle. When they find he merely wants them to look at crystals he's discovered, their rebellion so angers him, he uses his atomic generator to shrink them to just a foot high. Now they must escape his wrath and the creatures of the jungle as they battle to reverse the process.