Using Built-In Light Meter
Every modern digital still and video camera has built-in light meter. Whenever the camera switches to fully automatic or to semi-automatic mode, it uses the light meter to calculate best exposure settings, such as lens aperture, shutter speed and amplification level (gain).
In fully automatic mode, the camera calculates all three parameters. In semi-automatic mode the camera calculates only those parameters that are not locked by a user. For example, in Shutter Priority mode the user selects shutter speed, while the camera calculates lens aperture and gain. In Aperture Priority Mode the user selects lens aperture, while the camera calculates shutter speed and gain.
Oversimplified Exposure Control
Many point-and-shoot camcorders - like last year's Elura 100 - went further down the road of simplification, disposing of Shutter Priority and Aperture Priority modes. Instead they provide several recording programs called Scene Modes, like Sport or Portrait. A user does not need to select specific aperture or shutter speed anymore, the camera itself knows that wider aperture is preferred for portraits, and faster shutter speed is preferred for sports.
Along with simplified user controls, modern camcorders report back simplified information as well. Many consumer-grade camcorders do not provide basic exposure information, like current aperture or shutter speed. At best, they allow locking exposure and adjusting it up or down within limited range, using artificial exposure units called EV steps. The user is left completely unaware of what exactly happens behind the scenes.
Photographers Are Treated Better
Despite the evident trend to shield consumers from nuts and bolts of camera optics, when it comes to manual controls, the photographers are usually treated better than videographers.
Many Canon camcorders can take still photos and write them to a memory card. If you switch to card mode and press "photo" button halfway, the camera will often display current aperture and shutter speed in the lower right corner of the LCD/viewfinder. Sometimes you will need to insert an actual memory card in the card slot to obtain exposure information.
In auto-exposure mode the camera will choose all exposure parameters automatically based on measurements from the built-in light meter. If you lock one of the parameters, the camera will adjust others. Assuming that the camera meter works identically in the card and tape modes, you can set up exposure parameters for a still shot, then switch to video mode and roll the tape. The ability to obtain light meter information is the key to pseudo-manual mode of Canon camcorders.