resolve
To render visible or distinguishable the parts of something.
resolve: make two close things look like two things
To resolve is to separate and display two adjacent or overlapping objects as distinct in an optical image. A microscope resolves cells; a telescope resolves binary stars; a camera resolves fine print. Without resolution, nearby details blur together into a single smudge. With it, they appear as separate entities. This is not about magnification, which enlarges everything equally. Resolution is about the ability to tell things apart.
The limit to resolution is set by the wavelength of light used and the aperture of the optical system. The Rayleigh criterion, a standard measure, states that two point sources are just resolved when the central maximum of one diffraction pattern falls on the first minimum of the other. For visible light (roughly 400 to 700 nanometres) and a typical microscope objective, the practical limit lies around 0.2 micrometres. Shorter wavelengths, like ultraviolet or X-rays, permit finer resolution. Larger apertures also improve it, which is why astronomical telescopes have massive mirrors.
Variants and measurement
In microscopy, numerical aperture (NA) combines lens quality and working distance to define resolving power. A high-NA oil immersion objective might achieve 0.1 micrometres; a low-power objective cannot. In imaging sensors, resolution is often stated in megapixels or lines per millimetre, but pixel count alone does not guarantee true optical resolution; a poor lens wastes pixels. Electron microscopes resolve at the nanometre scale and below because electrons have much shorter de Broglie wavelengths than visible photons.
In spectroscopy, resolving power means the ability to distinguish closely spaced wavelengths or frequencies. A spectrograph with high spectral resolution can separate narrow emission lines that a coarse instrument would merge. The same principle applies: only fine enough separation produces distinct signals.
Users often confuse resolution with clarity, focus, or signal-to-noise ratio. A sharp, focused image may still fail to resolve fine structure if the optical system lacks sufficient aperture or wavelength. Conversely, a well-resolved image may appear grainy or noisy if sensitivity is poor. In practice, resolution limits what you can see; other factors determine whether you see it well.