A tensioned foil scaled Pepper's ghost to concert-size stages

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Two patents for the same idea, filed the same day

On 1 April 2004, inventors Ian O'Connell and James Rock filed both an international application, published as WO2005096095A1 on 13 October 2005, and a US filing that issued six years later as US7883212B2. The international filing names Musion Systems Ltd as applicant; the granted US patent lists Anakando Ltd as current assignee, a reminder that ownership in this field has moved between corporate vehicles even as the underlying claims stayed the same. Both documents describe the same apparatus: a projector, a frame, and a screen held under tension at an angle to the projector's beam.

A foil instead of a sheet of glass

The screen is described as typically a polymeric foil, which can have a partially reflective coating, inclined at approximately 45 degrees to the horizontal and capable of being rolled about a cylinder when not in use. A projector mounted overhead directs light downward onto a grey or coloured reflective board at stage level, which redirects the image upward onto the inclined foil. Because the foil is only partially reflective, a performer standing behind it remains visible to the audience while the reflected image appears to float in the space in front. Tensioning straps around the frame, some fitted with an abrasive grip, are adjusted individually to remove wrinkles that would otherwise break up the reflection, and a hinged reflective member compensates for keystone distortion introduced by the projector's angle.

Still a reflection, not a reconstructed wavefront

Both patents are explicit that the resulting picture is a virtual image created from light reflected from the screen, appearing to be located behind the screen. That is the same optical description John Henry Pepper gave of his glass-and-hidden-stage arrangement in 1862, engineered for scale: a thin, tensioned, semi-transparent surface replaces a large pane of glass, and a video projector replaces a lit set. Nothing in either document describes wavefront reconstruction, parallax, or a genuinely three-dimensional image. The virtual image is flat and only correct from within the audience zone the 45-degree geometry was designed for; move far enough to the side and the reflection distorts or disappears, and ambient light bright enough to compete with the projector washes it out.

• Is the screen a tensioned foil at an angle, or an LED wall? The two fail differently in bright rooms.
• What is the usable viewing cone before the reflected image visibly distorts?
• Who currently holds the patent rights, and does that affect which productions can legally use this exact rig?

The engineering in these filings is real and specific: foil tensioning, keystone correction, projector placement. But it describes a delivery mechanism, not a new form of imaging. Any show built on this patent family is doing Pepper's ghost with better materials, and its own claims say so.