The US company Wollensak made a series of lenses that were designed to photograph traces on the CRT screens of oscilloscopes. These lenses were fast, since the traces are dim, optimized for closeup work–from half to full life size–and with a strong negative field curvature in order to keep all parts of the convex oscilloscope screen in sharp focus. That makes these lenses pretty much useless for normal photography, but gives them very unique and strong bokeh characteristics. There are Oscillo Raptars, Oscillo Anastigmats and Oscillo Amatons. I am not familiar with the latter two, but it appears that the Raptars have the strongest field curvature. In those, two different versions were made, one for closer work at 1:0.9x and another at 1:0.5x. They do give slightly different renderings.
As one stops the lens down, the strange bokeh diminishes and eventually disappears. With this lens at f1.9 the effect is very strong, and I have found that generally I like the effect most between f2.8 and f4. It is also possible to reverse the lens, which makes the effect even stronger. Have a look at these. The effect is not to everyone’s taste, but I find that it is often very pictorial in quality.
