Mini Physics
Part of Mini EducationSwitch subject
SearchBookmarksMenu

Describing lens images

Key idea: A real image forms where rays meet and can be caught on a screen; a virtual image forms where rays appear to come from. Compare heights for size and orientation for upright or inverted.

Reading settings

On this page

Reading settings

Text size, line spacing and reading width for your lessons.

Text size
Line spacing
Reading width

Live preview

Take a moment to read at your own pace. Choose the text size and spacing that feel comfortable for you.

Pause after each idea, then explain it in your own words before moving on.

Narrower lines take effect when the screen has room.

Enlarged diagram

A camera, a projector and a magnifying glass all use a converging lens, yet the camera’s image is tiny, the projector’s fills a wall and the magnifier’s cannot be caught on a screen at all. Three pairs of words describe any image, and each pair is decided by its own piece of evidence. You do not need to draw lens ray diagrams or remember which image goes with each object distance.

Describe an image from the evidence

A lens can form many different images. Describe each one with a word from each of three pairs. Decide each pair from its own evidence.

The three pairs of image characteristics and the evidence for each

PairEvidence to look for
Real or virtual

A real image forms where rays actually meet, so it can be caught on a screen. A virtual image is where rays only appear to come from; you see it by looking through the lens, and a screen cannot catch it.

Magnified or diminished

Compare the image height with the object height. Bigger is magnified; smaller is diminished. Equal heights: the image is the same size.

Upright or inverted

Compare the way up. The same way up as the object is upright; upside down is inverted.

If no image appears on the screen, check its position and the illumination. Use the ray paths or full description to decide whether the image is virtual.

One word does not tell you another. “Real” does not mean diminished, and “magnified” does not mean virtual: read the evidence you are given for each pair.

How real and virtual lens images differPanel A: two rays from the same object tip pass through the lens. The actual outgoing rays intersect on the far side at a screen, giving a real, inverted, magnified image. Panel B: two rays from the same object tip pass through the lens. The actual outgoing rays diverge. Their dashed backward extensions meet on the object side, giving a virtual, upright, magnified image. The parallel ray passes through the far focus; the central ray passes straight through C. Ray arrowheads show actual light travel; object and image arrows show orientation. The dashed extensions have no travel arrows.A: Real imageSolid rays: actual light paths. Dashed lines: backward extensions.principal axisscreenobjectreal imageC: optical centreB: Virtual imageSolid rays: actual light paths. Dashed lines: backward extensions.principal axisobjectvirtual imageC: optical centre
How real and virtual lens images differPanel A: two rays from the same object tip pass through the lens. The actual outgoing rays intersect on the far side at a screen, giving a real, inverted, magnified image. Panel B: two rays from the same object tip pass through the lens. The actual outgoing rays diverge. Their dashed backward extensions meet on the object side, giving a virtual, upright, magnified image. The parallel ray passes through the far focus; the central ray passes straight through C. Ray arrowheads show actual light travel; object and image arrows show orientation. The dashed extensions have no travel arrows.A: Real imageSolid rays: actual light paths. Dashed lines: backward extensions.principal axisscreenobjectreal imageC: optical centreB: Virtual imageSolid rays: actual light paths. Dashed lines: backward extensions.principal axisobjectvirtual imageC: optical centre
Thin-lens ray constructions: actual rays meet at real images; backward extensions locate virtual images. Vertical distances are enlarged, so ray angles are schematic.

Positions and image heights follow the ideal thin-lens model, with rays changing direction at the lens’s centre plane. The principal axis and backward extensions carry no travel arrows. Panel A shows actual rays meeting on a screen; in B, only their backward extensions meet. These are two examples of image evidence, rather than a table of object-distance cases to memorise.

Worked example 1

Describing the image in panel A

Problem

Describe the image in panel A of the figure, giving the evidence for each word.

Show full solution

  1. Real or virtual

    Method

    Look at where the rays go after the lens.

    Reason

    If they actually meet, the image is real and a screen can catch it.

    Working

    Answer

    The rays meet at the screen: real.

  2. Upright or inverted

    Method

    Compare the arrows.

    Reason

    The object arrow points up; the image arrow points down.

    Working

    Answer

    Inverted.

  3. Magnified or diminished

    Method

    Compare the heights of the image and object arrows.

    Reason

    Image size is decided independently of whether rays meet.

    Working

    Answer

    The image arrow is longer, so the image is magnified.

  4. Give the complete description

    Working

    Answer

    The image is real, inverted and magnified.

Check your understanding 1 Panel B

Describe the image in panel B of the figure. Give the evidence for its type, orientation and size.

Show answer

Virtual: the rays spread out after the lens; only their backward extensions meet. Upright: the image and object arrows point the same way. Magnified: the image arrow is longer than the object arrow.

Guided practice 2

Your turn: camera, projector and magnifying glass

About 6 min

Problem

Use the evidence in each description to classify the image. A camera lens forms an image of a tall building on the small light sensor at the back of the camera; the image on the sensor is upside down. A projector lens forms a picture on a large wall screen from a small slide, and the slide must be loaded upside down for the picture to appear the right way up. Through a magnifying glass, a stamp looks bigger and the right way up; a screen held anywhere behind the lens shows no image.

Try this before viewing the solution

The image on the camera's sensor is:
The projector's image on the wall, compared with the slide, is:
The image seen through the magnifying glass is:

Hints

Hint 1

real or virtual

Which observation tells you whether actual rays meet?

Hint 2

the other two pairs

Compare size and way up with the object each time: the building, the slide, the stamp.

Show solution step by step

  1. Camera

    Method

    Sensor, much smaller than the building, upside down.

    Reason

    Each piece of evidence settles one pair.

    Working

    Answer

    Real, diminished, inverted.

  2. Projector

    Method

    Wall screen, much bigger than the slide, upside down compared with the slide.

    Reason

    The comparison is always with the object, here the slide.

    Working

    Answer

    Real, magnified, inverted.

  3. Magnifying glass

    Working

    Answer

    The stamp appears bigger and upright through the converging lens: virtual, magnified, upright. A virtual image cannot be formed on a screen.

Check your understanding 2 Real means small?

A 2.0 cm object forms a sharp 6.0 cm image on a screen. A student says one of these measurements must be wrong because a real image must be smaller than its object. Use both observations to evaluate the claim and describe the image’s type and size.

Show answer

The screen image is real because rays actually meet there. It is magnified: 6.0 ÷ 2.0 = 3.0, so it is three times the object’s height. These observations are compatible; real images can be magnified. They do not give the orientation, which needs its own observation.

Common mistakes

  • Saying a real image is always diminished. Real or virtual depends on whether rays meet, not on size.
  • Saying every image formed by a converging lens is real and inverted. A magnifying glass gives a virtual, upright image.
  • Calling an image virtual because it is small or dim. Any image caught on a screen is real.
  • Forgetting the third possibility for size: an image the same height as the object is neither magnified nor diminished.

Spotted an error? Report a correction

Syllabus and review details

Last reviewed:

Back to top