>>4191421The entire camera has to be made of a magnesium frame for basic durability with a DSLR or a MILC. Pretty much all cameras, even the shittiest sony and fuji, have magnesium frames.
Even if the mirror, mirror box, associated motor, pentaprism, and AF sensor array and associated mirrors/prisms weighed nothing (they don't, it's probably a half pound all together), it would still be slightly heavier just because the frame would be bigger to fit all of that shit.
