--- title: "Magnifiers, Microscopes and Telescopes" description: "An optical instrument can use an objective to form an intermediate image and an eyepiece to enlarge its apparent angle. Microscope magnification combines linear and angular factors. Telescope magnific" canonical: https://lightmysky.com/learn/science/magnifiers-microscopes-and-telescopes-mt_f30rUsqYkN source: https://lightmysky.com/learn/science/magnifiers-microscopes-and-telescopes-mt_f30rUsqYkN.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Magnifiers, Microscopes and Telescopes An optical instrument can use an objective to form an intermediate image and an eyepiece to enlarge its apparent angle. Microscope magnification combines linear and angular factors. Telescope magnification, field of view, light collection and resolution describe different properties. Subject: Science · Area: Waves, Light & Sound · Ages 19 to 21 Page: https://lightmysky.com/learn/science/magnifiers-microscopes-and-telescopes-mt_f30rUsqYkN ## Ready when they can - Traces an object through a two-lens instrument and computes the overall magnification - Distinguishes linear from angular magnification and says which matters for a distant object - Explains why a large aperture helps a telescope in two separate ways ## Lesson: Images through optical instruments Linear magnification compares image height with object height. Angular magnification compares viewing angles with and without an instrument. A converging lens with an object inside its focal length gives an upright, enlarged, virtual image. A magnifier lets you view an object closer than your unaided near point while keeping its image in focus. Near points vary; calculations here use the conventional reference distance D = 25 cm. For a magnifier or eyepiece with its final image at infinity, the small-angle rule is M = D/f. The eye can then view with relaxed focusing. If the lens is close to the eye and the final image is at the near point, use M = 1 + D/f instead. State the viewing condition and use matching distance units. For D = 25 cm and f = 2.5 cm, infinity viewing gives M = 10. *(drawing: The final image is at infinity, so this calculation uses D/f.)* Model a compound microscope with two converging lenses. The specimen sits just beyond the objective's focus. The objective forms a real, enlarged, inverted image well beyond that focus. This intermediate image becomes the eyepiece's object. Place it at the eyepiece's object-side focal plane for a final image at infinity, or inside that focal length for a finite virtual image. The eyepiece preserves the intermediate image's orientation. The objective's linear factor is m_obj = -di_obj/do_obj. Multiply it by the eyepiece's angular factor: M_total = m_obj × M_eye. For m_obj = -12 and M_eye = 10, the product is -120. Its magnitude is the angular enlargement relative to viewing the specimen unaided at D. Its negative sign means inverted. Objective focal length alone does not determine objective magnification. *(drawing: Image-relay stages, not ray paths. For infinity viewing, the intermediate image is at the eyepiece's focal plane.)* A telescope objective receives nearly parallel rays from a distant object and forms a real image at its focal plane. In a two-converging-lens telescope, align this plane with the eyepiece's object-side focal plane for a final image at infinity. Then M = -f_obj/f_eye in the small-angle model. Its magnitude is f_obj/f_eye; the minus sign means inverted. This compares the same distant object's viewing angles with and without the telescope. For a fixed eyepiece apparent field, increasing magnification reduces the true field on the sky: approximately, true field = apparent field/|M|. A larger-looking image need not reveal finer detail. Magnification and resolution differ. A reflecting telescope uses a curved mirror, rather than a lens, to form the intermediate image. An eyepiece can then enlarge its apparent angle. A larger clear aperture collects more light and permits finer diffraction-limited detail. For comparable unobstructed telescopes, collected light scales with diameter squared: doubling diameter gives four times the light. At the same wavelength, the diffraction-limited minimum angular separation scales as 1/diameter, so doubling diameter halves it. Atmospheric blur and optical defects can limit the actual gain. **Recap.** Follow the intermediate image and state the viewing condition. Multiply microscope factors. Keep telescope magnification, field of view and resolution separate. *Lesson, questions and flashcards written for this dataset. OpenStax texts were consulted for physics facts; textbook passages are not reproduced.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Curved Mirrors, the Mirror Equation and Real Images](https://lightmysky.com/learn/science/curved-mirrors-the-mirror-equation-and-real-images-mt_7XqB2umthJ) - [Thin lenses and the lens maker's equation](https://lightmysky.com/learn/science/thin-lenses-and-the-lens-makers-equation-mt_FXOcC5mpIM) ## Optional connections - [How Telescopes Work](https://lightmysky.com/learn/science/how-telescopes-work-mt_-SZU6cVB_-)