Practice question

Abbe's diffraction limit defines that light cannot be focused below roughly half wavelength divided by numerical aperture. For visible light around 500 nm and high NA oil objectives of 1.4, lateral resolution approximates 0.61 λ/NA, yielding ~200 nm, while axial resolution depends on refractive index and is poorer, near 500-700 nm. This barrier arises because overlapping Airy discs prevent distinguishing closer points. Understanding this physical constraint explains why organelle details below 200 nm require super-resolution or electron microscopy, guiding choice of imaging modality in cell biology curricula.