I see this A7R shutter shock has been mentioned on here before:
Richard Karash suggested either flash or “The other approach to shutter shake is a really long exposure (so the shake portion is a very small part of the exposure). ISO 100, f/8 might give 1-3 sec with your light panel.”
I see also that someone using an A7R2 found the mechanical shutter ‘useless’ and had to use the electronic shutter, presumably because there was some camera shake creeping in on their setup even with that camera.