Methods and systems for sequencing a nucleic acid molecule are described that comprise imaging a first surface and an axially-displaced second surface using a compensation-free optical system, the system comprising an objective lens and at least one image sensor, wherein said optical system has a numerical aperture (NA) of less than 0.6 and a field-of-view (FOV) of greater than 1.0 mm2; and) processing the images of the first surface and the axially-displaced second surface to correct for optical aberration such that the images of the first surface and the axially-displaced second surface have substantially the same optical resolution.