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If you zoom in on a digital photo forever, it doesn't reveal hidden secrets β€” it just dissolves into a blurry grid of colored squares.
Microscopes face this exact limit: magnification (how large an image appears) is completely useless without resolution (the minimum distance between two points at which they can still be seen as separate entities).
Why can't light microscopes simply use stronger glass lenses to zoom in on individual DNA strands?

The Physics of Resolution

In 1873, German physicist Ernst Abbe discovered that a microscope's resolution is fundamentally limited by the wavelength of the radiation used β€” the physical distance between repeating wave crests.
Because visible light has wavelengths between 400Β nm400\text{ nm} and 700Β nm700\text{ nm}, light waves diffract (bend) around any object smaller than about half their wavelength, capping a light microscope (LM) at a maximum resolution of roughly 200Β nm200\text{ nm} (0.2 μm0.2\,\mu\text{m}) and practical magnifications of around 1,500Γ—1{,}500\times.
If light waves are physically too wide to resolve tiny organelles like ribosomes (20Β nm20\text{ nm} across), how do biologists see them?

Electron Microscopy: TEM vs. SEM

Instead of light rays and glass lenses, electron microscopes use accelerated beams of electrons focused by electromagnets.
Because high-velocity electrons have wavelengths thousands of times shorter than visible light, electron microscopes achieve resolutions down to 0.1–0.2Β nm0.1\text{--}0.2\text{ nm} and magnifications exceeding 1,000,000Γ—1{,}000{,}000\times.
A Transmission Electron Microscope (TEM) passes electrons through an ultra-thin sliced specimen to reveal 2D internal ultrastructure, while a Scanning Electron Microscope (SEM) bounces electrons off the specimen's surface to create 3D topography.