I was looking at this comparison when I realised the camera on the left had a 2.0 crop in a mirrorless body made in 2012 while the camera on the right was full frame, had a mirror and was made in 1972. Notice the size difference there.
Now if you want to compare that same camera to a modern Digital camera with a full frame sensor and a mirror, you're looking at something like this. Notice that size difference.
I can't quite understand why that is. The main arguments I've seen for this is (1) electronics and (2) ergonomics.
I don't buy this argument. Surely we don't need that much space to fit the electronics in this day and age where a dual core CPU, dual core GPU computer logic board is about the size of your thumb.
I don't buy this argument either. Just look at the rise in popularity of mirrorless systems these days. This is not because people prefer EVFs to TTL OVFs (most would still like a good OVF given the chance), it's because these mirrorless systems are much smaller. Clearly the demand for smaller is there, no matter how much people say that bigger cameras are more ergonomic.
So in 40 years of technological progress, we've managed to match the size of a camera from the 70's only after ripping out the pentaprism and putting in a much smaller focal plane. Seems silly, no?