The application of surface plasmonic effects in engineering of a wavelength-tunable silver nanolens for the beam focusing is considered. Its design includes flat nanoslits for phase and amplitude modulation of light beams. Initially its operation has been checked for light beams with a wavelength of about 1.3 µm by observing the variance in the focal point distance with respect to alterations in structural parameters, such as the metal thickness, slit width, and pitch. The near-field intensity with respect to deviation in the focal point and deflection from the mean power for an optical 100-nm window is estimated for other popular optical communication wavelengths (0.85 and 1.55 µm) using the finite-difference timedomain method with boundary conditions for anisotropic, perfectly matched layers. The novelty in the proposed lens is its capability to function satisfactorily for a tolerance range of ±2.5% in the design parameters for the wavelengths under consideration.