Raw already is compressed. My 40D takes raw files around 12 to 15 MiB. They vary in size, so that's a first clue. Also, if you do the math, 14 bits per channel

Raw already is compressed. My 40D takes raw files around 12 to 15 MiB. They vary in size, so that's a first clue. Also, if you do the math, 14 bits per channel on those images comes out around 65 MiB.