Hi Dan,

You have run into one of the difficult situations that yes a faster lens is going to make a big difference, and I would suggest a fresnel as well, as Don mentioned, our glass is very smooth and allows a better distribution of light, but is not the solution to every single situation that can occur, I would expect any light measurement to be 1.5 to 2 stops brighter by adding the fresnel to any type of glass screen, you might try the less expensive route and add a fresnel first, but my suggestion, would to be get the faster lens, as f/8 is a slower lens and does not let as much light in as the faster lenses.

Good luck and good shooting.

Dave Parker
Satin Snow Ground Glass