What's the problem with using taper as a descriptive? It's just the relationship between the front and back curvature of the lens to ensure that you're looking through the same amount of lens material whether you're looking straight forward through the lens or at a more oblique angle of incidence through the extremities. It's why many aftermarket lenses that aren't base in prism or taper-corrected have distortions at the corners.Yes prism. Taper is a very poor description of the relationship of the front and back lens surfaces. $52 for a polar prism is pretty cheap. Not sure of the actual clarity under a Stenograph but I can say for sure a plain non colored quality polycarbonate prism compensated lens blank from Zeiss is more than that price. At cost. Revants non HC3 lenses are NOT prism based.