ABSTRACT
Large-format production requires large-format film. Multiple images had already been ruled out and it was considered impractical to attempt to develop a new format absolutely from scratch. However, there had already been a good deal of production done in the 65 mm/70 mm format – 65 mm for shooting, 70 mm for projection – and stock was available right out of the Kodak catalogue. 65 mm film is employed in various conventional formats including Todd-AO, Super and Ultra Panavision, but the image size on the film is restricted by the available width between the sprocket holes to 48.5 mm. Imax realized that just as the VistaVision format turned 35 mm film sideways to allow a wider image, 65 mm could be turned sideways too, so that the width of the image could be allowed to extend over 15
sprocket holes to 69.6 mm. The area of a large 15-perf frame is therefore some 3376 mm2, which is more than three times the area of a conventional 5-perf 65 mm frame, and more than ten times the area of 35 mm. Comparisons with 16 mm are, I feel, rather superfluous and video – even digital video – doesn’t even enter the arena. One would be entitled to ask why the 15-perf width was chosen rather than a greater or lesser figure. Apparently it had to do with the manufacturing process in which the perforations of the film display cyclical slight irregularities. 15-perf works, but increasing the width further apparently did not work so well. Also, the 15-perf width of 69.6 mm gives an aspect ratio a little bit wider than 4:3 which corresponds well with the human field of vision in the vertical and horizontal directions. If earlier large image films had used widescreen to trick the eye into thinking it was seeing something spectacular, IMAX presentations didn’t need it – it was just huge! It is probably fair to say that IMAX production accounts for the bulk of 65 mm and 70 mm stock sold right now, conventional 65 mm production currently being something of a rarity.
