We propose a novel focusing scheme to achieve approximately depth-invariant lateral resolution and signal to noise ratio along an extended axial scanning range for in vivo high-resolution imaging. The pupil function of the objective lens is modulated with a series of radial gratings implemented with a spatial light modulator. Each grating gives rise to a parabolic phase aberration that shifts the focal volume with a pre-defined distance along the optical axis. Dynamic focusing is readily achieved without mechanical translation of sample or focusing optics. With spatial light modulator of higher respond time, images acquired with different focal positions can be fused to retrieve a high-resolution image with depth-invariable lateral resolution and signal to noise ratio.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.