How many times have you heard it said, "You should never look at the camera"? There's a belief that even a cursory glance in the direction of the lens can break the illusion, for those watching, of being a fly-on-the-wall.
Media trainers routinely advise people doing press interviews to avoid looking at the camera, (or up or down or to the side), but rather fix your eye contact on the interviewer - you are more likely to appear self-conscious and unresponsive to the interviewer's questions if you start looking at a blank lens.
At the same time, many documentary makers would actually prefer that their subjects looked out from the screen directly at us. A shot from an angle may convey an air or impartiality that suits daily news interviews and suchlike, but it doesn't carry the same intensity that comes from being face-to-face.
The problem is that in an interview situation the subject still reacts best when interacting with an interviewer, rather than with, as documentary-maker Errol Morris puts it, "a piece of glass with a diaphragm behind it".
Morris has been grappling with this issue ever since he made his first of seven documentaries, Gates of Heaven, about a Californian pet cemetery, in 1978.
When doing interviews for the film, he wanted the subject to be looking as directly at the camera as possible so that the audience would share "the moment of drama", where the subject makes direct eye contact with the interviewer.
However, even though he put his head right up against the camera lens, interviewees were looking at him a bit off to the side. He also found that his head would creep into shot and his cameraman would yank his neck to pull him back.
After one too many yanks, he began to wonder, "What if the camera and myself could become one and the same?" The solution was an interviewing machine called, in true Buck Roger's parlance, The Interrotron.
A system of modified Teleprompters, it allows Morris to project his image on a monitor placed directly over the camera's lens. Interviewees address Morris's image on the monitor while looking directly at the camera, which lets Morris and the audience achieve eye contact with his subjects.
The effect is to focus the subject's attention and gaze more directly into the camera than was possible in the past. "It's the difference between a faux first person and the true first person," says Morris.
Although politicians and newscasters use Teleprompters so that they can read text and look into the lens of the camera at the same time, it lacks the human connection.
"A newscaster looking into the camera is not looking at anyone. He is simply looking into a dead lens," says Morris.
"If there's a prompter, the situation is no better. Now, he's simply looking into the "face" of dead copy, verbiage, lines on a page, the prompter version of text splayed out in readable form."
With the Interrotron, the subject interacts with the live projection of the interviewer on the camera lens.
Morris used his Interrotron extensively when he directed two seasons of the television series, First Person, and in his documentaries. The only person who has objected to the Interrotron was former US Secretary of Defence Robert McNamara during the filming of The Fog of War, although he was sufficiently at ease to offer some startling revelations about the Cuban Missile Crisis, the Second World War in the Pacific and the Vietnam War.
"He's so used to doing interviews in a different way," says Morris. "He came in to the studio and saw this contraption and said, "What is this?" I told him it was my interviewing device, and he said, "Whatever it is, I don't like it." But then he sat down and never complained after that."