A converging lens bends light inward to meet at a focal point. A diverging lens spreads light outward. The difference in behaviour comes down to shape: the converging type is convex (thicker in the middle), while a diverging lens is concave (thinner in the middle). This one shape difference determines everything — how they focus light, what kinds of images they form, and where they are used. Here are the 3 key differences between them.
Think of a converging (convex) lens as an optical funnel. It gathers light from across its surface and directs it to a single spot. A diverging lens is the opposite — like a spray nozzle — it takes the light that enters and spreads it wide. Both are essential, but they solve opposite problems.
What is a converging lens?
A converging lens (also called a convex or positive lens) is thicker in the centre than at the edges. When parallel light rays pass through, they refract twice — entering and leaving the glass — and the curved shape bends them inward toward the centre line. The rays meet at a single point called the focal point on the far side of the lens.
The distance from the centre of the lens to the focal point is the focal length. For a converging lens, the focal length is always positive. A more curved lens has a shorter focal length and bends light more sharply. A flatter one has a longer focal length and bends more gently.
Converging (convex) lenses are the workhorses of optics. They are used in cameras (to focus a scene onto the sensor), telescopes (to gather and focus light from distant stars), microscopes (to magnify tiny specimens), magnifying glasses, and eyeglasses that correct farsightedness (hyperopia).
What is a diverging lens?
A diverging lens (also called a concave or negative lens) is thinner in the centre than at the edges. When parallel light rays pass through it, the curved shape bends them outward away from the centre line. The rays spread apart on the far side and never actually meet. If you trace the diverging rays backward, they appear to come from a virtual focal point on the same side as the incoming light.
The focal length of a diverging lens is always negative. A stronger diverging lens (more curved inward) has a shorter negative focal length and spreads light more widely.
Diverging lenses are less common as standalone components but indispensable for specific jobs. They correct myopia (nearsightedness) by spreading light before it enters the eye, give a wide-angle view in door peepholes, and expand narrow laser beams into wider, safer beams.
3 key differences between converging and diverging lenses
1. How they bend light
A convex lens bends parallel rays inward so they meet at a real focal point on the far side. A diverging lens bends parallel rays outward so they appear to come from a virtual focal point on the near side.
2. The images they form
A convex lens can produce both real and virtual images depending on where the object is placed. Place the object beyond the focal length and you get a real, inverted image — the kind that falls on a camera sensor or a cinema screen. Place it inside the focal length and you get a virtual, upright, magnified image — exactly what a magnifying glass does.
A diverging lens always produces a virtual, upright, and diminished image, no matter where the object sits. The image is always on the same side of the lens as the object and is always smaller than the object. This is why you can never project a diverging lens image onto a screen.
3. Their focal length sign
A converging (convex) lens has a positive focal length (e.g., +10 cm). A diverging lens has a negative focal length (e.g., −10 cm). The sign tells you instantly which type you are dealing with. The lens formula 1/f = 1/v − 1/u works for both, but the sign of f determines the behaviour of the image.
How to tell a converging from a diverging lens
You can identify the type without any equipment.
By touch. Run your finger across the surface. If the centre bulges outward, it is a converging (convex) lens. If the centre dips inward, it is a diverging (concave) lens.
By sight. Hold the lens at arm's length and look through it at a distant object or text. If the object appears larger, the lens is converging. If it appears smaller, the lens is diverging.
By the focal length sign. If you know the focal length from the manufacturer or a prescription, a positive number means converging and a negative number means diverging.
The BBC Bitesize guide on convex and concave lenses provides detailed ray diagrams showing exactly how the two types refract light. The Physics Classroom tutorial on refraction by lenses walks through the three principal rays step by step for both lens types.
Common misconception: "lenses always magnify"
Many people assume that a convex lens always produces a magnified image because they have only seen one used as a magnifying glass. In fact, this lens type produces a diminished image whenever the object is placed beyond twice the focal length — that is how a camera fits an entire mountain onto a small sensor. The same lens can magnify, reduce, or produce same-size images depending on where the object is placed.
The opposite myth applies to diverging lenses: "a diverging lens always makes things tiny." While it is true that a diverging lens always produces a diminished image, the amount of diminishment varies with object distance. A very close object through a weak diverging lens may look only slightly smaller.
For a more detailed comparison between the two shapes, see our guide on concave vs convex lens. For the full details on how each type works, read the convex lens guide and the concave lens guide. The physics of how both types bend light is explained in our article on how lenses use refraction.
Frequently Asked Questions
What is a converging lens?
A converging lens is a convex lens that is thicker in the middle than at the edges. It bends parallel light rays inward so they meet at a single point called the focal point. Converging lenses have positive focal lengths and can form both real and virtual images.
What is a diverging lens?
A diverging lens is a concave lens that is thinner in the middle than at the edges. It spreads parallel light rays outward so they appear to come from a virtual focal point on the same side as the incoming light. Diverging lenses have negative focal lengths and always form virtual, upright, diminished images.
Is a converging lens concave or convex?
A converging lens is always convex — thicker in the middle and thinner at the edges. The convex shape bends light inward to a focal point. A concave lens (thinner in the middle) would diverge light, not converge it.
Is concave diverging or converging?
A concave lens is diverging. Its thin centre and thick edges cause light rays to spread outward rather than meet at a point. The mnemonic to remember this is: concave caves in and diverges; convex bulges out and converges.
What type of image does a converging lens produce?
A converging lens can produce both real images (when the object is beyond the focal point) and virtual images (when the object is inside the focal point). Real images are inverted and can be projected onto a screen. Virtual images are upright and appear on the same side of the lens as the object.
What type of image does a diverging lens produce?
A diverging lens always produces a virtual, upright, and diminished image — regardless of where the object is placed. The image is always on the same side of the lens as the object and cannot be projected onto a screen.
About Umar Farooq
Umar Farooq writes in-depth guides on the physics of light and optics — from reflection, refraction, and lenses to diffraction, lasers, and fiber optics, explained from first principles.
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