As a general rule with an HD source on an HD display you can sit as close as 1.5 times the screen width. For a 50" diagonal display this works out to be 5.5 feet. However, plasma displays have a pixel structure and I find it best to be seated far enough away so that this structure is no longer visible. What distance this occurs depends on the specific plasma you select (the resolution, pixel size, and pixel pitch, or spacing, are the key items to consider) and this distance will also depend on your own eyesight. Even people with 20/20 vision will vary in their perception of a visible pixel structure. With the highest resolution 50 plasmas the pixel structure should start becoming invisible at a distance of perhaps 7 to 9 feet, but I suggest you visit some stores and check it out for yourself.
Ron Jones
Ron Jones