There were three aperture control options to Apo Nikkors. All the later ones had both multi-bladed circular apertures and a Waterhouse slot accepting different shapes or potentially a gel filter at the nodal plane. But there was also a version of the 360 at least, which had both round and square adjustable apertures. Square would be in relation to best repro quality of actually square dots, versus the conventional round ones. I'm speaking about the top-end 4-element airspaced Apo Nikkor, not their cheaper line of process lenses used in conjunction with basic "stat cameras". Although these Apo Nikkors are very precise, and were exceeded only by their even higher priced Apo El Nikkor line, they have an unpleasant "double-lined" out-of-focus background blur characteristics or bokeh, just like many Nikon 35mm lenses of the past. For that kind of thing, a thick element tessar design is preferable. My own is a Zeiss 360/9 tessar barrel process lens. It's plenty sharp, but also has a lovely soft background blur. So, if selecting from older Nikon process lenses, you might want to look for an equivalent tessar formula - or just buy a Fujinon L tessar already in shutter.