The detection limit of surface plasmon resonance (SPR) measurements has been improved by a factor of approximately 2-3.5 if the angle of incidence was near to the reflection minimum of the SPR resonance curve instead at the position of the steepest slope, the standard alignment in SPR imaging. The enhancement of the detection power, a result of signal-to-noise optimization, is demonstrated by applying a photodiode and a CCD camera for SPR detection. The experimental data are compared with data expected from theory.