Resolving power is inversely proportional to the wavelength of the 'probe' used.

• Visible light has wavelengths of $\sim 400-700\text{ nm}$, limiting resolution to $\sim 200\text{ nm}$.
• Fast-moving electrons have a de Broglie wavelength ($\lambda =h/p$) that can be $100,000$ times shorter than visible light.
• This drastically increases the Resolving Power, allowing us to see details at the atomic scale.