ORF file are generated by Olympus cameras.
It if a TIFF file with a custom magic at the beginning:
IIRS instead of the TIFF magic.
IFD 0 contain the main image. IFD 1 contain the 160x120 preview. Some file don’t have the preview outside the MakerNotes.
Another peculiarity is that StripOffsets and StripByteCounts are arrays for the E10 files, unlike the others. Still consistent with the TIFF/EP standard.
Sometime the CFA does not look like it is compressed but seems to be organised weirdly. E400 has uncompressed CFA.