Panoramic camera mode
From Halopedia, the Halo wiki
Panoramic camera mode, commonly shortened to Pan Cam, is a feature that Bungie and 343 Industries added to Halo 3, Halo 3: ODST, Halo: Reach, Halo 4, and Halo: The Master Chief Collection. It is used by many players as a way to force the camera out of any map while in the Theater, and its use is permitted for screenshots, Film Clips, and other files.
Show coordinates/camera mode
The Show Coordinates mode displays the exact location of the camera, its rotation (in degrees), its speed, and the current camera mode. Pan Cam itself cannot be enabled until coordinates are displayed.
Reading the coordinates
Coordinates are displayed in white, sans-serif font, aligned to in the upper-left corner of the screen. The coordinates consist of three space-separated numbers, followed by a slash, followed by two more space-separated numbers, another slash, another number, and then either "[normal]" or "[pan-cam]". Here is an example of coordinates that may be shown:
The first three numbers are coordinates showing the camera's exact position in the map, relative to the map's centerpoint. The first two coordinates are the camera's lateral position; the third coordinate is the vertical position. You can never go farther than ±50000.000 world units from any map's center, though no map's playable area ever comes close to that size.
The next two numbers show the camera's angle of rotation in degrees. The first value shows your lateral orientation—if it's 0, you're looking east; if it's 90, you're looking north. The second value is your vertical orientation—if it's 0 or 180, the camera is level; if it's 90, the camera is looking straight up; and if it's -90 or 270, the camera is looking straight down.
The third number is the camera's speed, which can only be adjusted while in Pan Cam mode. Following that is the current camera mode.
Uses for coordinates
Coordinates can be useful when taking aerial photos of a map, to identify which way is north. They can be used to measure distances, as one world unit equals to ten feet. By taking note of the coordinates of an area in a Campaign level's cutscenes, it is also possible to "break into" the areas in the cutscenes when using the Pan Cam to glitch the camera outside the level boundaries (as described below). All cutscenes are rendered in real time, so all areas shown in cutscenes have to be hidden somewhere in a level. As an example, the coordinates above are where you can find the Ark as seen from space in the opening cutscene of the level of the same name -- it's hidden beneath the level boundaries. Near the start of that same level, you can also find the Shadow of Intent's bridge, hidden behind a cliff face.
Pan Cam is little more than a set of alternate controls. These alternate controls, however, provide a previously-hidden function—the ability to change the camera's movement speed—that can be used to force the camera outside a level's boundaries.
To activate Pan Cam, first turn on Coordinates as described above. Then, press and hold LB + RB + LS + RS + D-Pad LEFT. The "[normal]" at the end of the coordinates should change to read, "[pan-cam]". You can also enable Pan Cam by simply viewing any Film Clip that was saved while in Pan Cam. Pan Cam will remain enabled either until you disable it or until your session ends (you exit or turn off the game).
The controls in Pan Cam are somewhat altered. The bumpers on the controller are now useless; LT is used to descend and RT is used to ascend. The left stick still controls your movement, but it cannot be used to move vertically, even if you are looking upward or downward. Up and Down on the D-Pad will increase and decrease your speed. Pausing is still Available using the A button.
Glitching the Pan Cam outside a level's boundaries
Pan Cam's main use is its is primarily used to force the camera out of a level's boundaries.
To do this, you must watch a Film in which a player either falls to their death or dies while in Edit Mode. Focus the camera on that player, and then pause the Film and detach the camera when the player dies. Then, approach, but not touch, the "target" boundary. Raise the camera's speed to a very high value (something around 50,000.000 will work), and either quickly flick the left stick towards the boundary (if it's a wall) or quickly press the appropriate trigger (if it's an invisible floor or ceiling). The result will be that you clip through the wall and over to the other side.
(If the camera is following a living player, then it will snap back to that player after any attempt to exit the level's boundaries.)
To ensure that you've paused at the right time, "detach" the camera from the player by pressing Y, move the camera away a small distance, and then press Y again; if the HUD appears, but the camera does not move, then you are now free to force the camera outside the map. Note, though, that sometimes, Y will return the camera to your character, but the camera can still be forced out of the map.
Make sure you reduce your speed after exiting the map, to make it easier to explore outside the map!
Things to note
There are a number of caveats and issues when working outside the level boundaries.
Basic instructions for multiplayer maps
Instructions for campaign maps
Note: Not all levels can be used for Pan Cam.