The camera must be made for manipulating it, lenses, too. I have mainly to do with movie cameras. Most of them are, say, okay to handle, if not equal, and some are more equal. In my eyes focusing is the most critical affair of photography and cinematography, so a stigmomètre would be most valuable. The stigmomètre is the invention of Lucien Dodin, 1943, a couple of invertedly arranged slant prisms, the split screen. Exposure somewhat off you can do something about later, object out of focus—never.
Astonishingly movie cameras don’t have prism screens. They have a ground glass or a focusing prism with a ground surface. You can see them through from big to small, Panaflex-Arriflex-Aaton-Eclair-Mitchell-Bell & Howell-Konvas. The first Canon Scoopic had a prism screen, better Super-8 cameras have one. Filmo 70-DA and later models have a 15 times magnifying GG critical focuser. Eyemo have a GG focuser just like the Standard camera had. Paillard-Bolex H have a ground prism focusing system. Beaulieu Reflex a ground planoconvex lens. Pathé WEBO M have a planoconvex lens with a central ground area on the convex side. Ciné-Kodak Special GG, hardly magnified. Kodak Reflex Special GG with 10 and 20 times magnification. Soviet cameras have GG focusing as well, some very finely etched (technology transfer from the USA) and well magnified. The Arriflex 16 ST has a thin GG. Older models have thorium oxide glasses in the finder that turn brown and cut heavily on brightness. The Pentaflex 8 has an aerial image, the manual advises to set focus by the distance scale of the lens!
Lenses should be well maintained so that focusing goes easily, lightly. I may not be as fast as an AF system but I see what I’m setting the focus on and I can discern between fences and foilage and things. AF systems are often fooled.