7 Introduction to Multi-Camera Filming
Even though the impression of multiple camera coverage can be obtained with the use of a single camera using multiple takes and ‘cutaway’ shots (see Post Production – section 2.5 The Cutaway), there are many situations where the use of multiple cameras is desirable or even essential. These include situations where you want to give your audience better coverage of a live event or to shorten the production time. For instance, when recording interviews that require reaction shots from the interviewer or audience it might be quicker or more appropriate to use more than one camera.
The most important thing is for the videographer to ensure that both or all cameras are producing matching pictures. This includes technical aspects such as the picture quality, colour balance and picture ratio. When filming interviews, drama and other subjects where you are trying to unify the viewer’s POV (Point of View), you must also pay attention to aesthetic values such as camera angle, length of lens, shot size and the line of action.
The first stage of matching images is to use the same make and model of camera – or at the very least to use cameras which can be adjusted to produce precisely the same image quality as each other. Secondly, these cameras must be set up in exactly the same way, with respect to colour balance, shutter speed and exposure. Any variation of these settings will be noticed by your audience as you cut from one camera to another.
7.1 Live-Mix versus Post-Mix
There are two methods of mixing footage from different cameras to create one programme stream; either live-mixed or post-mixed. Live-mix is the process of taking a feed from different cameras through a vision mixer and then on to a recorder. Post-mix is the process of using separate cameras, recording each output locally and then editing the separate recordings into one programme stream in post production.
Each process has its benefits and drawbacks, and the videographer can also use a combination of these techniques by live-mixing and simultaneously recording the output from each camera separately (via ‘isolation feeds’ also known as ‘ISO feeds’), so that recordings from each camera can be used in post production to compensate for any errors made during the live-mix.
The main benefit of a live-mix is that it will save time in post production. It might also be the only solution if the output has to be simultaneously transmitted to an audience via large screen projection, website stream or traditional terrestrial or digital broadcast. However, the main drawback of live-mix is that it requires additional manpower in the form of a director to ‘call the shots’ and control the vision mixing.
To facilitate this, channels of communication between the camera operator and the director will be needed (via a headset intercom system or ‘talkback’) and, ideally, a return programme feed to each camera so that they can individually see what is being recorded and/or transmitted. Also ‘tally’ lights (the red indicator light found on top of all high-end cameras) enable the operator, and the subject being recorded, to see precisely when the camera is live (or ‘on shot’).
7.2 Cables & Connections
A live-mix will require extensive cabling or other means of sending the output of the camera back to the vision mixer. Studio-configured cameras may also require cables for both video signals and and ‘genlock’ (general-locking) signals. Genlocking signals are used to sync (or time) the cameras together so that the vision mixer can cleanly cut between signals.
Standard composite video cable lengths should be kept to a maximum of 100m, otherwise amplification will be required. Likewise, multi-core camera cables have a maximum length of 300m. For cable lengths in excess of 300m the videographer will need to use cameras with Triax connections, which are generally only found in broadcast environments.
7.3 Stage Lighting & Colour Balance
Regardless of whether you are live-mixing or post-mixing, you will need to ensure that each camera is producing the same colour balanced image. This can be particularly problematic at indoor events with mixed or coloured lighting falling on the subject, such as stage performances.
In these situations Auto White Balance should not be used as it will result in a varying colour balance between cameras. The best practice for setting a common colour balance between cameras is to do the following:
- Prior to the performance or event, ensure that all house-lights are switched off (particularly fluorescent or sodium lights) and ask the lighting technician to turn on un-gelled (un-coloured) theatre lamps, or use your own lighting if this is not possible.
- Then use a white card on centre stage to set each camera’s white balance manually. This might require you to initially move the cameras close to the stage so that white balance can be set.
- The cameras should then be left in manual white balance mode and at this setting throughout the performance. If this is not possible then the second best course of action is to use all the cameras in their pre-set tungsten light mode.
7.4 Length of Lens
To help position characters in space, when using more than one camera or filming position to film interaction between characters in an interview or dramatic scene, you should use the same focal length of lens and shot size (known as ‘matching shots’). You can, of course, use a different length of lens or shot size on an establishing shot, cutaway or for dramatic effect, but once you start to film the interaction between characters, the opposing shots should again be matched in focal length and shot size.