>>3790385>The pentaprism, mirror and mechanism are able to be squeezed into an Olympus OM2 sized body made in the 80s.No AF motor, no AF sensors, a mechanical shutter, no built in flash, no sensor and associated circuit board (much thicker than film), no memory card slots, no usb connectors, rudimentary light metering, a battery the size of a coin, no optical viewfinder adjustment. Take a film SLR apart sometime, the mechanical shutter is a wonder to behold, beautifully engineered and miniaturized, but there just isn't that much inside of the camera. A light metering circuit that a first year EE student can design, a couple of wonderfully complex mechanisms for the shutter and mirror lift, and the gears which advance the film and the exposure number indicator. Most of the camera is empty space without a roll of film in it, and a roll of film takes up a lot less space than a decently sized battery, a sensor, an image processing board, a memory card board, an AF sensor array, etc. Common components like the mirror and pentaprism are of fixed dimensions governed by physics and the size of the sensor, an APSC mirror is fairly small, but a FF mirror is bigger, the mirror must sit at 45° to the sensor plane to direct light upward, setting a minimum size requirement for the space between flange and sensor, the APSC camera can't reduce this distance unless it is to use dedicated lenses.
Compactness is a huge selling point for cameras, Sony leans heavily on the compactness and light weight of its mirrorless offerings. Do you think all the marketers and bean counters and engineers just ignore the opportunity to sell the most compact SLR because they don't want to try hard enough and make it smaller? Modern entry level DSLRs are fucking tiny btw, they're easily as small as the compact AF SLRs of the '90s.
