B

Resolving power (minimum distance d that can be distinguished) is governed by Abbe’s equation d = 0.61 λ / NA, where NA (numerical aperture) depends on the objective/condenser aperture and refractive index; thus it is influenced by aperture size and by the wavelength of the illumination. The focal length of the eyepiece only affects image magnification after resolution has been set by the objective and therefore does not determine resolving power [Murphy & Davidson, 2012, PMID 22511620; Inoue & Oldenbourg, 2016, PMID 27019365].