Seems like I am always trying to improve my focusing options, not just on my Rolleiflex, but also on all my older cameras and particularly on my LF cameras.
There are a lot of factors to consider from the type of glass to the grit and process used, acid treatment, optical coatings, and then of course fresnels are almost their own subject. Lens fit to the camera can also affect the type of screen and fresnel you might want.
I understand different types of glass will behave differently and most of the screens are made from soda lime glass but there are many alternatives.
I’m currently working on a screen for my 11×14 inch custom built camera and am using a soda lime glass blank hand ground by Steve Hopf with a projection TV fresnel situated between the ground glass and the lens.
I’m going to start this post now and fill it out as I have time.
For now some reading links: