Differences between ST500 and ST550 While ST 500 has a smaller LCD screen at 3”, the LCD screen of ST 550 is larger at 3.5”. ST 550 has more vibrant colors at 1152k, whereas you get 230k colors with ST 500. ST 500 is lighter at 149gm, whereas ST 550 weighs 165.7gm. ST 500 is slightly thinner in comparison to ST 550.