system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Whats the difference from those big bulky cameras you'd see at movie sets and tv shows ,and the normal small portable cameras?
gpt
The main reason is those cameras carry physically larger lenses and the sensor inside the camera is larger as well. These are larger both to enhance quality and to work well in low light situations, such as when actors are talking indoors. They also have a bit more electronics to send a lower quality version of the video over a radio link, across the stage to where the director typically watches on a large monitor, and technicians record this temporary version so the director can play it back as many times as they like to decide if the shot was ok. 

The lenses are engineering marvels themselves. They have geared focus rings so the focus is controlled by a second operator. Different focal length lenses from the same manufacturer have the focus rings in the same place so the lenses can be quickly swapped without having to realign the focus mechanism.