Yes, it must only seem to shallow the field when focusing. I had always assumed it was at least partially from a shallower depth of field along with the ability to more clearly focus and assure the focus by virtue of the brighter image.
Not only that, but when a screen is optimized for a slower aperture, focusing accuracy suffers. For example, when I mount my FD 85mm f/1.2 to my AE-1 Program, I find it very difficult to focus accurately on a subject, whereas if I mount that 85mm on my F-1, I can focus with ease. It appears that the AE-1P can handle lenses as fast as f/1.4 without problems, but that additional 2/3 stop is just too much for it.
My old F-1s both have the later Laser matte screens. I don't recall the letter designation, but they're plain matte screens in both cameras. The New F-1 has the Partial plain matte screen also -- don't recall it's model designation either. I don't believe any of them are optimized specifically for fast lenses.
My old F-1s both have the later Laser matte screens. I don't recall the letter designation, but they're plain matte screens in both cameras. The New F-1 has the Partial plain matte screen also -- don't recall it's model designation either. I don't believe any of them are optimized specifically for fast lenses.