As for the Kinetoscope itself, there is a significant disagreement over the location of the shutter providing the crucial intermittent visibility effect. According to a report by inventor Herman Casler described as "authoritative" by Hendricks, who personally examined five of the six still-extant first-generation devices, "Just above the film...a shutter wheel having five spokes and a very small rectangular opening in the rim directly over the film. An incandescent lamp...is placed below the film...and the light passes up through the film, shutter opening, and magnifying lens...to the eye of the observer placed at the opening in the top of the case." Robinson, on the other hand, says the shutter—which he agrees has only a single slit—is positioned lower, "between the lamp and film". The Casler–Hendricks description is supported by the diagrams of the Kinetoscope that accompany the 1891 patent application, in particular, diagram 2. A side view, it does not illustrate the shutter, but it shows the impossibility of it fitting between the lamp and the film without a major redesign and indicates a space that seems suitable for it between the film strip and the lens. Robinson's description, however, is supported by a photograph of a Kinetoscope interior that appears in Hendricks's own book.