Oh, and why are Heliars a certain speed? Well, that probably has to do with the maximum aperture at which reasonable quality could be obtained and the practicality of building a lens of a certain size at the time it was produced. My 360/4.5 Heliar is huge and weighs several pounds without a shutter! Some shorter Heliars and heliar copies like the Kodak Medalist Ektar 100/3.5 lens are f:3.5 lenses. There is also an Ektar 105/3.7, which is a heliar type.