I'll add one thing that I haven't seen mentioned anywhere - you can stack fresnel lenses, which adds their individual refractive effects. This is good for wide angle lenses and can give you a remarkably even illumination with ultra-wide lenses, even in low-light conditions.... just experiment to find with what works for you. The downside is that the corners get messed up and there can be a bit of an interference pattern between the 2 sets of grooves. I had one setup which was a Beattie intenscreen, which has its own built-in fresnel, and then I would add another fresnel on top when using wide angle lenses.

Jim