Complex sentence: To reach speeds as high as 1/500 second the inertia of the thin vulcanite shutter disc had to be kept at a minimum, requiring a small-diameter disc with a minimal sector opening.
Split into simpler sentences: To reach speeds as high as 1/500 second, the inertia of the thin vulcanite shutter disc had to be kept at a minimum. This meant a small-diameter disc with a minimal sector opening.