Magnifiers, Microscopes and Telescopes
Instruments are built by putting lenses in sequence so that the image of one becomes the object of the next, and angular magnification is what the eye actually notices. A telescope trades field of view for resolution and light collected.
What a learner can do afterwards
- 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
1 · Read
A convex lens can work as a simple magnifier. Hold it so the object sits inside its focal length, and you get an image that is upright, enlarged, and virtual. It looks bigger because it fills a wider angle in your eye than the object would at your near point, about 25 cm away.
A compound microscope chains two convex lenses. The objective has a short focal length and forms a real, enlarged, inverted image just past its focus. The eyepiece acts as a magnifier on that image, with angular magnification of 25 cm divided by its focal length when the final image sits at infinity. The total is the product of the two: one setup with a 6 mm objective and a 50 mm eyepiece gives minus 186, and the minus means the final image is inverted.
A telescope chains two lenses the other way round. The object is so far away that its rays arrive nearly parallel, and the objective forms a small real image at its focal plane. The eyepiece magnifies only that image, so the telescope trades a wide field of view for a bigger angle on a distant thing. What matters here is angular magnification, roughly the objective focal length divided by the eyepiece focal length.
A wide aperture helps a telescope twice. It collects more light, so faint objects show up, and its wider opening resolves finer detail.
Chain two lenses so the first image becomes the second lens object, and judge the result by the angle it fills in your eye.
2 · Watch
Take it off screen
Where it sits
Learn first
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.