In the movie Modern Times, Charlie Chaplin appears to come dangerously close to falling to his death, this gif shows how the scene was actually shot using what's known as a "glass shot." A similar technique was used in the original Star Wars when Kenobi is shutting down the tractor beam.
I wonder how they did the panning in the shot, since the elements wouldn't line up if you moved the camera. Shot the full frame and then panning across the already recorded footage? Seems like a tricky thing to do when you're purely analogue. @shootER got any ideas?
With the foreground painting that close to the lens there shouldn't be much, if any, parallax error when the camera pans. Doing a dolly or zoom would be problematic, but using a pan should allow the effect to be done in-camera.
"Glass Matt" is the proper term. I think "Foreground painting" or "Foreground Matt" is also acceptable.
That's what I don't understand, I would have assumed that the glass being closer to the lens would result in more parallax error.
Well close in relative terms. It has to be close enough to hide the fact that there's just a floor next to Chaplin, but far enough away so the depth of field is roughly consistent so the trick is believable. Too close and either the foreground is in focus or the background is in focus, not both. The same if the camera is too far away: the depth of field is even more shallow. In the sweet spot you can make it so each is enough in focus to pull off the gimmick (as long as you throw enough light on the subjects so that the f-stop is at a high number).
My friends and I tried it in super-8 back in the 80s, for a spoof episode of In Search Of. On the cheap. We used a glass storm door clamped to a saw horse. I drew a pyramid, cut it out and taped it to the door. For a glorious moment, there was an Egyptian pyramid on the Hackensack skyline. And our reflections in the glass. And one of the actors raised his hand too far and it went behind the pyramid...
