The Germans actually had a bifocal scope in service in WWI, called "Zeiss Glasvisier 16". It was attached to the rear sight (therefore adjusted with the rear sight) and for better sighting it had a front sight cap with self-illuminating material.
I'm attaching some pictures of one of my Glasvisier mounted on a Gew98. I have some more pictures of the carrying pouch as well, but can only post 10 pictures per post. If someone wants them, I could add them in another post.