---
title: "Single-Slit Diffraction and the Limit of Resolution"
description: "One slit spreads light into a wide central maximum with weaker ones either side, and the narrower the slit the wider that spread. The same spreading fixes the smallest detail a telescope or an eye can"
canonical: https://lightmysky.com/learn/science/single-slit-diffraction-and-the-limit-of-resolution-mt_qiG0fGadBU
source: https://lightmysky.com/learn/science/single-slit-diffraction-and-the-limit-of-resolution-mt_qiG0fGadBU.md
retrieved: 2026-09-12
---

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# Single-Slit Diffraction and the Limit of Resolution

One slit spreads light into a wide central maximum with weaker ones either side, and the narrower the slit the wider that spread. The same spreading fixes the smallest detail a telescope or an eye can separate.

Subject: Science · Area: Waves, Light & Sound · Ages 17 to 18
Page: https://lightmysky.com/learn/science/single-slit-diffraction-and-the-limit-of-resolution-mt_qiG0fGadBU

## Ready when they can

- Describes how the pattern changes as the slit width or the wavelength changes
- Contrasts the uneven single-slit pattern with the even fringes from two slits
- Explains why a larger aperture separates finer detail

## Lesson: One slit spreads, wide eyes resolve

One narrow slit does not paint a sharp stripe. Light spreads into a broad bright centre with fainter fringes that fade fast either side. Make the slit narrower and that central band grows wider. The parts of the wavefront mix after the gap to make this shape.

Longer wavelengths spread more, so red paints a broader pattern than violet through the same gap. Short blue light stays tighter. This is why colour order matters whenever you read a pattern.

Two slits tell a different story: a comb of evenly spaced fringes of similar height. That regularity shouts two sources. No lens beats its own blur either: when one centre lands on its neighbour, detail merges. Bigger apertures narrow each blur, so wide mirrors split finer stars.

**Recap.** Narrow gaps spread light wide, colour sets the width, and wide apertures rescue fine detail.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Coherence and Young's Double-Slit Fringes](https://lightmysky.com/learn/science/coherence-and-youngs-double-slit-fringes-mt_mONvXhPmwq)
- [The Diffraction Grating and Measuring Wavelength](https://lightmysky.com/learn/science/the-diffraction-grating-and-measuring-wavelength-mt_yIjB-uJuFt)

## Opens up

- [Intensity in Single-Slit and Double-Slit Diffraction](https://lightmysky.com/learn/science/intensity-in-single-slit-and-double-slit-diffraction-mt_HURhzZdIkM)
- [Flux, Magnitudes and the Distance Ladder](https://lightmysky.com/learn/science/flux-magnitudes-and-the-distance-ladder-mt_q1vEUas3AY)
- [Photon Energy and the Electronvolt](https://lightmysky.com/learn/science/photon-energy-and-the-electronvolt-mt_UfmDhGRaYT)
- [de Broglie Waves and Electron Diffraction](https://lightmysky.com/learn/science/de-broglie-waves-and-electron-diffraction-mt_Y8NthsmPcv)