Optical spatial resolution improvement using local focused ion beam (FIB) assisted silicon material removal was investigated. Two types of test structures were chosen for imaging-resolution characterization to be able to use two ways of measuring resolution. Samples of various remaining bulk silicon thicknesses were prepared and characterized in terms of image quality and spatial resolution. The resulting remaining bulk Si thickness was measured using reflectance spectrometry. Images were acquired using halogen-lamp illumination and reflected light detection using a cooled Si-CCD detector. To investigate the image quality at various wavelengths, a set of interference band-pass filters was applied.