My Yashica Mat uses standard Rollei bayonet filters; I have a Rolleisoft I diffusion filter, and I decided to try it out. It has a series of circles on the glass which cause bright highlights to go all glowy, although the effect is very subtle and generally lost if you stop down or use contrasty film. It's a far cry from the double fog filters of Geoffrey Unsworth (and on a practical level you have to unmount the filter in order to put the lens cap back on) but it's there, lurking. Could the effect be achieved with Photoshop? Yes. Yes, it could. Also, the Mat's negative area is definitely taller than it is wide. It's 6x6-and-a-bit.
