A speckle-based trackball apparatus with an optical architecture employing curved-wavefront illumination beam or a modified imaging lens and aperture configuration is provided. The apparatus includes a trackball configured to be rotated by a user. In the curved-wavefront embodiment, an illuminator is configured to illuminate a spot area of the curved surface of the trackball with a curved-wavefront illumination beam so that an ensemble of optical features used for motion sensing interact with the illumination beam at different phase points as a function of a location within the illuminated spot area on the curved surface of the trackball. In the modified imaging lens and aperture configuration, the aperture is positioned between the back focal plane and the image plane of the imaging lens, and the illuminator may be configured to illuminate a portion of the trackball with a planar-wavefront illumination beam. Other embodiments, aspects and features are also disclosed.