That is probably their first model of optical sight ("scope"). I had a more conventional looking model also called the "Solar" that was in the 800 serial number range. The tube was about 1.5" diameter and about 10" long IIRC. The prism cover was similar to this one, but did not project as high above the tube. I see this scope has no serial number, at least not where mine did, on the prism cover, which would indicate earlier production than mine I think.

This one has been re-blued IMO, and of course the cross hairs are not original.

According to a Zeiss corporate website I saved a copy of a few years back, the first Hensoldt prismatic appeared in 1902 and was the first prismatic sight released. I believe the Zeiss prismatic scopes started in 1903.