No such thing as too small for a rangefinder. As long as there is any sort of parallax between the 2 optic ports, then it can be used as a stereoscopic rangefinder.
You get much more accurate readings the farther apart the 2 are, which is why you typically get those massive ones on tanks that don’t have to worry about weight, but when space is an issue, then you can go for a smaller system than none at all. The Conqueror also mounts it’s rangefinder in the cupola rather than spanning the whole turret.
Conqueror is a bad example and is from the mid-50’s, which is why I neglected to add it. We’re talking about a vehicle from 1945. The Conqueror also has a coincidence rangefinder, not stereoscopic which is why it’s much smaller.
The problem with smaller stereoscopic rangefinders is that the smaller they are the less accurate they are.
Stereoscopic is really something you want as large as possible to get the most accuracy for your weapons effective range, here it is compared to other systems.
