The image of an object placed at infinity with a convex lens is formed precisely at its focus.
Understanding Image Formation by Convex Lenses
Convex lenses, also known as converging lenses, are thicker in the middle and thinner at the edges. Their primary function is to converge parallel rays of light that pass through them. When an object is positioned at an extremely great distance—effectively considered "at infinity"—the light rays arriving from it are parallel to the principal axis of the lens.
As stated in the reference Image Formation by Concave and Convex Lenses: "When an object is placed at infinity, the real image is formed at the focus." This fundamental principle applies directly to convex lenses. Because convex lenses have a real focus (where light rays actually converge), they are capable of forming a real image of a distant object at this point.
Characteristics of the Image Formed
When an object is at infinity, the image formed by a convex lens exhibits specific characteristics:
- Location: Formed at the principal focus (F) of the lens.
- Nature: It is a real image, meaning it can be projected onto a screen.
- Orientation: It is an inverted image.
- Size: The reference further clarifies that "The size of the image is highly diminished and point size." This means the image is extremely small, often appearing as a single point.
Here's a quick summary for clarity:
| Object Position | Image Position | Image Nature | Image Size |
|---|---|---|---|
| At Infinity | At the Focus | Real, Inverted | Highly Diminished (Point Size) |
Practical Applications
This principle is crucial in various optical instruments:
- Telescopes: The objective lens of a refracting telescope forms a real, inverted, and highly diminished image of distant stars or planets at its focal plane. This image is then magnified by the eyepiece.
- Cameras: When focusing on very distant subjects (e.g., landscapes), a camera lens adjusts so that the image sensor or film is positioned at or very near its focal point to capture a sharp image.
- Projectors (Inverse Principle): While not directly image from infinity, understanding the focus is key. If a light source is placed at the focus, the lens produces a parallel beam of light, which is useful in floodlights or projection systems.
Understanding how convex lenses handle light from infinity is fundamental to the design and function of many optical devices that allow us to observe and capture images of the world around us. For more in-depth knowledge about lens properties, you can explore detailed optics resources Learn More about Lenses.
