The frameline of an S2 is a thin etched line for a 50mm lens, not unlike the Leitz SBOOI-finder but darker, because it is also the window of the rangefinder. When the glass system is clean, it is quite bright. The finder is 1:1 and has no distortion.
When using a 35mm lens, the best you can do is to use a SBLOO-finder from Leitz. The Nikon 35mm bright line finder is good, but the frameline does not anticipate on the distortion of the optical system of the finder as the SBLOO does.
Erik.