What limits resolution in electron microscopy despite short wavelengths?
Theoretical resolution in electron microscopy benefits from picometer electron wavelengths at high accelerating voltages, but practical resolution is constrained by lens aberrations and aperture. Angular aperture limits collection of scattered electrons; small apertures improve contrast but reduce diffraction-limited resolution, while spherical aberration of electromagnetic lenses prevents perfect focusing. Unlike sample thickness which affects TEM contrast, aperture angle determines numerical aperture equivalent in Abbe equation for electrons. Advances like aberration correctors enlarge usable aperture, approaching atomic resolution. Thus beam strength or detector sensitivity alone cannot overcome fundamental optical limitations imposed by angular aperture.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.