Quote Originally Posted by Hops View Post
LXDUDE, I think you may actually mean "Fresnel" and not "prismatic". Microprisms are what's in the focus aid donut. Most newer viewfinders have a Fresnel etched into them to focus light towards the viewfinder instead of randomly like a ground glass screen does. I'm not sure when Nikon started using Fresnel screens.
It's definitely not fresnel. Fresnel lenses in viewfinders are concentric rings and are often faintly visible, but do not materially change the appearance of out-of-focus highlights. For example I can clearly see the fresnel rings in my Bronica's viewfinder with slow lenses but they don't affect the appearance of OoF images at all. They have been used for many many years and certainly precede the later Nikon screens.

The effect I'm talking about is somewhat like the effect given by the all-microprism screens I have for my Nikon F3, but finer.