Where is the ideal position for the mirror and projector in the dome?
There are no hard and fast rules but to maximise the dome coverage the mirror is normally placed quite close to the rim of the planetarium dome. This allows the majority of the dome to be projected onto, in reality the fact that 100% coverage isn’t generally achieved is not a significant problem if only because in most domes and most movie content is intended for directional seating/viewing. The position does depend on the dome orientation but the following two diagrams show the usual position for two extreme situations, a horizontal and a vertical dome.
