Spatially resolved optical imaging experiments were performed in a parallel plate reactor known as the Gaseous Electronics Conference Reference Cell. They consisted of recording the optical emission discharges at various pressures and powers for 1024 points across the electrode at a height of 7 mm above the bottom powered electrode for the argon neutral line at 750.4 nm. Previously, our experiments [Fender ct at, J. Appl. Phys. 74, 3590 (1993)] have shown that argon plasmas are nonuniform, specifically in the shape of annular rings with large intensities originating over the edges of the electrodes. In this work, we examined in situ the plasma uniformity as a single 3 inch silicon wafer with a simple test pattern was etched in a 30 seem CF4 / 15 seem Ar plasma environment. The results indicate that the plasma emissivity and etch depth are related. In the pressure range of 50 to 250 mTorr, the emissivity and the etch depth increase linearly with power. For a constant power, both emissivity and etch depth can be fitted to a quadratic polynomial with pressure as the dependent variable.