Sheet film sizes are either imperial (4x5", 5x7", etc.) or metric (9x12cm, 10x15cm, 13x18cm, etc.). They are not quite the same, with 4x5" being roughly 10.1x12.7cm, 5x7" being roughly 12.7x17.7cm, etc. Must the film and holder be exactly the same size, or can they be used interchangeably, for example 9x12cm film in a 4x5" holder, or 5x7" film in a 13x18cm holder? If I buy imperial sized holders, will I be able to use metric sized film? Thank you.