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What is Lens Magnification?

Published in Lens Optics 3 mins read

Lens magnification refers to how much larger or smaller a subject appears in an image compared to its actual size. Essentially, it's a measure of how much a lens can enlarge or reduce the apparent size of an object when it's projected onto an image plane, such as a camera sensor or film.

Understanding Magnification

According to the provided reference, the magnification of a lens is defined as the ratio of the image size to the object size. More specifically:

  • Image Size (Y): The length or size of the subject as it is captured by the lens on the image plane.
  • Object Size (X): The actual length or size of the subject.
  • Magnification = Y/X

This simple formula provides the magnification factor. A magnification value greater than 1 indicates an enlargement, while a value less than 1 represents a reduction.

Magnification in Practical Terms

Here's how to understand it in real-world scenarios:

  • Magnification > 1: The image of the object is larger than the object itself. For example, a magnification of 2 means the image is twice as large. This is common in macro photography, where you want to capture tiny objects in greater detail.
  • Magnification < 1: The image of the object is smaller than the object itself. For example, a magnification of 0.5 means the image is half the size of the object. This is common in wide-angle photography, where you capture a larger scene.
  • Magnification = 1: The image of the object is the same size as the object itself. This is considered 1:1 magnification, typically seen in macro lenses when capturing objects at their natural size.

Key Points to Remember

  • Magnification is a ratio: It's a relative measurement comparing image and object sizes.
  • Different lenses have different magnification capabilities: A wide-angle lens has low magnification, while a macro lens has high magnification capabilities.
  • Magnification is not the same as focal length: Focal length affects the angle of view; magnification affects the size of the subject within that view.
  • Image plane: Where the image is focused by the lens. This may be film or an image sensor.

Example

Let's say you're taking a photo of a coin that's 2 cm in diameter. In the resulting image, the coin measures 4 cm in diameter. Therefore, the magnification of the lens is:

Magnification = Image size (4 cm) / Object size (2 cm) = 2

This means the image of the coin is twice its actual size.

By understanding lens magnification, you can better select and use lenses to achieve your desired photographic results, from capturing tiny insects at large scale to wide landscapes with small subjects.