Regarding the shape of the "lens" - I spent a lot of time looking for old photos of the exterior of the lens of the sky periscope. Everything I found showed it was a vertical ellipse/oval. Although I guess to be honest, since the eyepiece was round, your view should be round and the advantage is that as you twist the handles you're changing the angle of the bottom mirror inside the scope, and therefore changing which part of the "oval" you're looking out of. However... I like this shape
