Is it used for some type of calibration? Something goes inside it? I see some sort of eye piece on the opened piece of 2nd pic.
Ding ding ding! We have a winner! This is a build up kit for an ENG TV camera. There are basically two types of cameras, the ENG and the studio cameras. The studio cameras have a large body with an way to attach the larger lens and are more expensive. Here is a studio camera: The ENG is what you usually see on a guy's shoulder with a little lens. Here is an ENG: Internally they are the same camera. So they have this build up kit that you can use to mount the ENG camera onto a large lens and to give you more control of it locally when it is mounted on sticks. It allows the TV production guys to buy a lot of the same camera and use them for hand held and fixed cameras. If one breaks, then they can swap them out as needed (different shows need different numbers of fixed and hand held cameras). Here is a picture of the ENG with the small lens removed and mounted in the build up kit:
