Lens and Focal Length

Lens and Focal Length

Lenses

  • A lens is a critical component of the camera that focuses light into the image sensor to create an image.
  • Lenses can be either fixed (attached permanently to the camera body) or interchangeable (can be removed and replaced with other lenses).
  • Interchangeable lenses provide more flexibility, allowing you to adapt to different shooting scenarios.
  • Lenses are categorized by their focal length, measured in millimetres (mm).
  • A lens with a short focal length provides a wide-angle view, whereas a lens with long focal length offers a narrow, zoomed-in view.
  • A prime lens has a fixed focal length, while a zoom lens has a range of focal lengths.

Focal Length

  • The focal length of a lens is essentially the distance between the lens and the image sensor when the subject is in focus.
  • It’s important to understand that focal length affects both the angle of view and magnification.
  • A short focal length (e.g., 18mm) captures a wide field of view with less magnification. This is ideal for landscape, architectural or interior photography.
  • A medium focal length (e.g., 50mm) gives a perspective similar to the human eye and is suitable for general-purpose photography.
  • A long focal length (e.g., 200mm) captures a narrow field of view with high magnification making them perfect for sports, wildlife or portrait photography.

Understanding Depth of Field

  • Depth of field relates to the degree to which objects in the foreground and background remain in focus.
  • Short focal length lenses have a greater depth of field, meaning more of the scene (from near to far) will remain in sharp focus.
  • Conversely, long focal length lenses have a shallow depth of field, allowing for a sharp focus on the subject while blurring out the background.
  • This technique called bokeh is often used in portraiture to draw attention to the subject.

Lens Speed

  • The speed of a lens refers to its maximum aperture, the largest opening that a lens can provide.
  • A lens with a large maximum aperture (e.g., f/1.4 or f/2) is considered a ‘fast’ lens as it can let in lots of light.
  • Fast lenses are ideal for low light photography and for creating a shallow depth of field.