Bigger, then upside down
How an object looks through a convex lens as it moves away.
Behind a magnifying glass
Look through a convex lens at a small object close behind it. It looks bigger. Now the object moves farther and farther away behind the lens.
What do you think happens to how it looks?
What this lesson covers
The idea
An object close behind a convex lens appears erect and enlarged; as its distance increases it appears inverted, first enlarged and then diminished.
Behind a magnifying glass
Look through a convex lens at a small object close behind it. It looks bigger. Now the object moves farther and farther away behind the lens.
What do you think happens to how it looks?
- At some point it turns upside down
- It keeps getting bigger
- It stays exactly the same
Look through the lens
Your eye looks through the convex lens. Move the object behind the lens from very close to very far. Watch how it looks.
Erect when close, inverted farther
An object close behind a convex lens appears erect and enlarged. As its distance increases, it appears inverted, first enlarged and then diminished.
This is just like a concave mirror. A magnifying glass is a convex lens held close to the object.
- Object behind the lens | How it looks
- Close | Erect, enlarged
- A little farther | Inverted, enlarged
- Far away | Inverted, diminished
Notes
An object close behind a convex lens appears erect and enlarged. Farther away, it appears inverted, first enlarged, then diminished.
Check yourself
A magnifying glass is held close to small print. How do the letters look?
An object moves farther and farther behind a convex lens. How does it look?
Through a convex lens, a tree far away looks…
- Inverted and enlarged. That happens when the object is a little farther from the lens.
- Erect and enlarged — correct. Yes. A close object looks erect and enlarged through a convex lens.
- Erect and diminished. Through a convex lens, a close object looks bigger, not smaller.
- It stays erect and the same size. That would be a flat glass plate, not a convex lens.
- It stays erect and keeps getting bigger. Beyond a short distance it turns upside down, and later it gets smaller.
- It turns inverted, first enlarged and then diminished — correct. Yes. That is what you saw.
- inverted and enlarged. That is when the object is only a little beyond close. Far away, it looks diminished.
- erect and enlarged. That is how a close object looks.
- inverted and diminished — correct. Yes. Far away: upside down and smaller.