Hi,
I have a Wista RF, and it uses what I think is the brightest, clearest screen I've seen on any camera. It is used with a plain gridded glass on top.
Unfortunately, the screen is a little too wide and short to fit onto my Technikardan.
It's very reasonably priced at $160, and I'd like to hear from anyone who knows of a similar quality third-party GG/fresnel at a similar price.

Thanks in advance