A little back story first. I bought a 5D, got the Ee-S screen for better manual focus with fast primes. Noticed that the viewfinder was considerably darker. Wondered if the Bill Maxwell Hi-Lux optical treatment that people rave about in other fora would do anything. So I bought a second Ee-S, send it to Bill, and got it treated. Got the treated screen today and thought I would run a comparison with the three screens. 5D was mounted on a tripod, pointed at a featureless, evenly-lit whiteboard. Nikon 85mm f1.4 AFD lens mounted (for ease of changing f-stop without having to hold the DOF preview, not enough hands), focused at infinity. Nikon Coolpix 4500 was held lens flat against the 5D viewfinder, manual exposure (1/8" f2.6), fixed focal length, fixed 100 ISO, fixed white balance, minimal adjustments, macro focus, fine JPG, no NR. The 5D focus brackets were centered in the 4500 finder for each shot. In photoshop, each shot was desaturated and three color picker points were selected (inside the center bracket, and just next to the left- and rightmost brackets), as close as possible to the same in each photo. The greyscale values measured from those points were averaged and plotted below versus the f-stops tested (f1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16). Looks like the stock Ee-A screen is about 2-2.5 stops brighter than the Ee-S, and the Maxwell Hi-Lux treatment is worth about 2/3-1 stop. Comments? Particularly on formatting the chart to make the comparison more clear?