Imaging of a 1mm circle of diatoms using the Marshall microscope. Objective #4 was used. Resolution is good except for obvious chromatic aberration. Note the shadows and lines. These are aberrations is the lenses of the instrument (grinding marks, surface depressions, etc).
Imaging the 2mm scale bar on a stage micrometer is much more problematic. The Marshall has no capability of modulating contrast (now achieved using a condenser diaphragm). Thus the extremely thin lines of the micrometer scale are poorly imaged. The overall magnification when using the #4 objective is approximately 20x.