Foxy, here is a link to the history of the SLR.
http://en.wikipedia.org/wiki/History...um_format_SLRs
I think we have become used to modern lightweight materials and so probably forget the limitations that early designers were faced with.
I remember the Topcon 35mm SLR of the mid 60's. Mirror shock and noise when tripping the shutter was plain frightening.
Don