Examples of Light Behavior Through Lenses: 3 Practical Examples You Can Actually See

Before touching a lab bench, look at the pair of eyeglasses on your desk. They’re one of the best examples of light behavior through lenses because you can see the effect instantly.

If you have nearsighted (myopic) glasses, hold them at arm’s length and look at a distant object through one lens. The object looks slightly smaller. That tells you the lens is diverging light—spreading rays out so that distant objects form a virtual image closer to your eye. If you’re farsighted (hyperopic), your glasses do the opposite: objects look slightly larger because the lens is converging light.

Under the hood, both are textbook examples of:

• Refraction: light bending as it crosses from air into glass and back into air.
• Focal length: the distance where parallel incoming rays either meet (converging lens) or appear to spread from (diverging lens).
• Image type: virtual images that your brain interprets as being at some distance in front of you.

In other words, every time you put on glasses, you’re running a live experiment in geometric optics.

2. Classic Lab Setup: Focal Length of a Converging Lens (Sunlight and a Screen)

If you want examples of light behavior through lenses: 3 practical examples that feel like “real physics,” this is the go-to starting point.

Setup

Use a simple converging lens (like a lab convex lens or a magnifying glass), a white card or wall as a screen, and sunlight or a distant streetlight as your source.

1. Hold the lens facing the distant light source.
2. Move the screen back and forth behind the lens until you see a sharp, bright image of the source.
3. Measure the distance from the lens to the screen. That distance is approximately the focal length \(f\) of the lens.

What you’re actually seeing

This is a clean example of light behavior through lenses because the incoming rays from a very distant source are nearly parallel. A converging lens bends those rays inward so they meet at the focal plane.

• The image is real (it appears on the screen).
• It’s inverted (upside-down compared to the object).
• The distance from lens to image is very close to \(f\) when the object is far away.

Mathematically, this matches the thin lens equation:

[
\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}
]

where \(d_o\) is object distance and \(d_i\) is image distance. For a distant object, \(d_o\) is so large that \(1/d_o\) is nearly zero, so \(d_i \approx f\).

If you want to compare your measurements to theory, you can look up refractive indices and lens formulas in open physics resources like OpenStax Physics (an open educational resource hosted by Rice University).

3. Moving the Object: Three Practical Image-Formation Cases with One Lens

Now let’s turn that one setup into three practical examples that show how image behavior changes as you move the object.

Use:

• A converging lens with known focal length (from the sunlight experiment).
• A small object (like an arrow on paper or an LED).
• A screen to capture the image.

Example A: Object Very Far Away (Object distance \(d_o \gg f\))

This is basically the sunlight case again, but you can repeat it with a distant building or tree seen through a window.

• Observation: The image forms at about one focal length behind the lens, inverted and smaller than the object.
• Physics: Parallel or nearly parallel incoming rays meet at the focal plane.

This is one of the best examples of how converging lenses create real images that can be projected.

Example B: Object Just Beyond 2f (Object distance \(d_o > 2f\))

Move a small object to a distance a bit more than twice the focal length from the lens and slide the screen until the image is sharp.

• The image forms between f and 2f on the other side of the lens.
• It is real, inverted, and smaller than the object.

This mirrors what happens in a simple camera focused on a distant subject. Light from the subject passes through the camera lens and forms a reduced, inverted image on the sensor.

Example C: Object Between f and 2f (Object distance \(f < d_o < 2f\))

Now move the object closer, somewhere between one and two focal lengths.

• The image forms beyond 2f on the other side.
• It is real, inverted, and larger than the object.

This is the optical geometry behind projectors: a relatively small object (or digital microdisplay) is placed between f and 2f, and the lens throws a magnified image onto a distant screen.

These three positions—far away, beyond 2f, and between f and 2f—give you a tight set of examples of light behavior through lenses: 3 practical examples all with one lens and one object.

4. Magnifying Glass: When a Converging Lens Makes a Virtual Image

So far, we’ve talked about real images on a screen. But one of the most familiar real examples of light behavior through lenses is the magnifying glass.

Try this:

• Take the same converging lens.
• Place a small printed word or a coin closer than the focal length to the lens.
• Look through the lens at the object.

You’ll see a virtual, upright, magnified image. There’s no way to catch this image on a screen behind the lens, because the rays leaving the lens are diverging. Your brain back-traces those rays and interprets them as coming from a larger object farther away.

This is:

• A textbook example of how converging lenses can produce either real or virtual images depending on object distance.
• The same geometry used in simple microscopes and jeweler’s loupes.

If you want to connect this to vision science, the National Eye Institute at the NIH has accessible explanations of how lenses and the eye work together: https://www.nei.nih.gov.

5. Diverging Lenses: Spreading Light and Correcting Nearsightedness

Most students see fewer hands-on examples of light behavior through lenses with diverging lenses, but they’re everywhere in real life.

Take a diverging (concave) lens and a converging lens with a longer focal length. Set up the converging lens to form a clear image of a distant object on a screen. Now slide the diverging lens between the converging lens and the screen.

You’ll notice:

• The image on the screen becomes blurred, then sharp again only when you move the screen farther away.
• That shift means the diverging lens has increased the effective focal length of the system by spreading the rays.

This is the same principle used in nearsighted glasses and contact lenses:

• The eye’s lens system focuses light too strongly.
• A diverging lens in front of the eye spreads incoming light slightly, so the combined system focuses light onto the retina instead of in front of it.

The American Academy of Ophthalmology and similar organizations explain these corrective-lens designs in more clinical detail; for a physics-first treatment, many university physics departments provide open lecture notes (for example, MIT OpenCourseWare at https://ocw.mit.edu).

6. Cameras and Smartphones: Modern, Real Examples of Lens Behavior

If you want 2024–2025 real examples of light behavior through lenses, your smartphone camera is probably the most relevant.

Multi-lens smartphone stacks

Modern phones use:

• Wide-angle lenses (short focal length) for broad scenes.
• Telephoto lenses (longer focal length) for zoom.
• Ultra-wide lenses for capturing more of the scene.

Each of these is a compact lens assembly designed to bend light so that it forms a sharp image on a tiny digital sensor. When you tap to focus, the phone physically shifts lens elements by fractions of a millimeter to change the image distance \(d_i\) and satisfy the thin lens equation for your chosen subject.

Portrait mode and depth of field

Another modern example of light behavior through lenses shows up in portrait mode. Optically, a longer focal length lens with a wide aperture produces a shallow depth of field: only a narrow range of distances is in focus, while foreground and background blur.

Phones now simulate this using both:

• Real lens behavior (aperture and focal length), and
• Software that uses depth maps to blur background pixels.

But the starting point is still geometric optics: how a real lens focuses light from objects at different distances.

The optical principles behind cameras—both phone and DSLR—are covered in many university physics and engineering courses. A readable overview of imaging systems can be found in materials from institutions like Stanford or MIT; for instance, MIT’s introductory physics and engineering optics materials on https://ocw.mit.edu connect ray optics directly to camera design.

7. Projectors and VR Headsets: Lenses in Immersive Tech

Two more real examples of light behavior through lenses that feel very 2024–2025:

Digital projectors

Modern classroom and home theater projectors still rely on the same optics you used in the earlier examples:

• A small, bright image (from an LCD or DLP chip) acts as the object.
• A converging projection lens places that object between f and 2f.
• The lens throws a magnified, inverted image onto a distant screen.

Engineers use the same thin-lens math, just with more complex multi-element lenses to reduce distortion and color fringing.

VR and AR headsets

Virtual reality headsets use short focal length converging lenses placed very close to small screens.

• The lens makes the tiny nearby screen appear as a large, distant virtual image.
• This reduces eye strain because your eyes focus as if they’re looking several feet away, not just an inch from your face.

This is a modern, consumer-facing example of light behavior through lenses: 3 practical examples all rolled into one device: magnification, virtual image formation, and field-of-view control.

8. Pulling It Together: Patterns Across All These Examples

Across glasses, magnifiers, cameras, projectors, and VR headsets, a few patterns show up again and again:

• Converging lenses can produce real, inverted images (when the object is beyond f) or virtual, upright images (when the object is inside f).
• Diverging lenses always produce virtual, upright, reduced images and are often paired with converging lenses in real systems.
• Focal length sets the scale: short focal length lenses give wide fields of view; long focal length lenses give magnification and narrower views.
• The thin lens equation remains a reliable, surprisingly simple tool for predicting where images will form.

If you step back, the best examples of light behavior through lenses are the ones you can observe daily: your vision correction, your phone camera, the projector in your classroom, and the optics in emerging AR/VR devices.

For more structured, college-level explanations and example problems, the free OpenStax physics text and many .edu resources give step-by-step treatments of these same systems.

FAQ: Common Questions About Examples of Light Behavior Through Lenses

What are three practical examples of light behavior through lenses I can test at home?

Three simple, testable setups are:

• Using a magnifying glass to find its focal length by focusing sunlight on a card.
• Creating an image of a distant object (like a tree or streetlight) on a wall with a single converging lens.
• Observing how a pair of glasses changes the apparent size and clarity of objects at different distances.

These are direct, hands-on examples of light behavior through lenses: 3 practical examples that match textbook ray diagrams.

What is an example of a virtual image created by a lens?

A classic example of a virtual image is what you see through a magnifying glass when the object is closer than the focal length. The object appears larger and upright, but you cannot project that image onto a screen. The image exists only in your line of sight.

What are some real-world examples of lenses in everyday technology?

Real-world examples include:

• Eyeglasses and contact lenses for vision correction.
• Smartphone and DSLR cameras for imaging.
• Projectors in classrooms and theaters.
• VR and AR headsets that make small screens appear distant and large.

All of these rely on the same basic rules of refraction, focal length, and image formation you see in simpler classroom experiments.

How do these examples of light behavior through lenses relate to the human eye?

The human eye is effectively a converging lens system focusing light onto the retina. When the eye’s lens system doesn’t focus light correctly, we correct it with additional lenses—glasses or contacts—that modify the path of incoming light. Organizations like the National Eye Institute (https://www.nei.nih.gov) provide accessible diagrams and explanations that connect these physics concepts directly to eye health.

Can a single lens explain how modern cameras work, or are they too complex?

Modern cameras use multiple lens elements, but the single-lens examples of light behavior through lenses still describe the core behavior: light from an object at distance \(d_o\) is brought to focus at distance \(d_i\) on the sensor. Extra elements correct distortion, chromatic aberration, and field curvature, but the basic focusing behavior matches the thin lens model you use in simple experiments.