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.

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.

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.

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.