Note 1: This calculator is only valid for flat films formats. It can't be
used to calculate the field-of-view of a true panoramic camera with
rotating lens.
Note 2: The sizes for 4.5x6 and 6x7 are the ones used by Pentax. Other
brands may have slightly different sizes.
Note 3: The sizes for large format are the nominal sizes. I think the
usable size is slightly smaller, but I don't have the exact sizes.