<p>Single-pixel microscopy is a computational imaging approach that produce images with a bucket detector by illuminating the sample with a sequence of micro-structured light patterns. In particular, Hadamard-based single-pixel microscopy (HSPM) is a leading implementation that uses Hadamard-basis patterns typically encoded on a digital-micromirror-device (DMD). Ultimate image quality and resolution depend on accurate demagnification of the patterns onto the sample, often requiring subwavelength projection resolution. However, aberrations introduced by DMDs, which are designed for consumer displays, together with sample scattering, constrain the HSPM maximum achievable performance under practical imaging conditions. In this work, the aberrations effects on HSPM are addressed, both theoretically and experimentally, thereby enabling HSPM near-diffraction-limited operation. The use of a multi-actuator adaptive lens to correct the aberrations effect on the projected patterns in HSPM is reported. A sensor-less method is developed to achieve aberration-free HSPM, leveraging direct frequency information from the sample Hadamard spectrum in a reconstruction-free approach. The proposed method is validated by correcting not only optical system but also sample’s induced aberrations, achieving near-diffraction-limit resolution. Consolidating the presented work as a framework that could play a major role in the development of single-pixel microscopy.</p>