While standing in the audience or by the mixer table I could create this sort of double exposure. First, I pointed the camera so that half of the frame was on the dark crowd, allowing the brightness of the stage to be exposed.

Then I turned the camera and exposed the other half a few seconds later. Here Freddie turns his head while his body stays in the same position, it created this nice line effect.

Photoshop didn’t exist in those days.

The first version came later in 1990.