The good thing about a fisheye lens is it takes cool round photos. The bad thing about a fisheye lens is all it takes are cool round photos, and one doesn't often need that ability. For a brief period around 1909-10, Mackenstein offered the Kallista camera. Designed by L. Stockhammer, as may be noted from the viewfinder, the camera was intended to take round stereo pairs, via a mask installed in front of the film plain. There was also a viewer designed for the round pairs, although I've never seen what it looks like. In 1913, Stockhammer wrote a scholarly treatise on stereo photography "Stéréoscopic Rationelle." Looking back through the lens of history, it would be interesting to learn the original rationale behind the Kallista design.