Digital Photography: Light, Sensors and Files
A short introduction to how cameras capture light and turn it into an image file.
Photography begins with light
A camera records light reflected or emitted by a scene. The lens focuses that light onto a sensor, and the camera controls how much reaches the sensor through aperture, shutter time and sensitivity settings.
These controls influence both exposure and appearance. A longer shutter time can show motion blur; a wider aperture can reduce depth of field; and higher sensitivity can help in low light while increasing visible noise.
The image sensor
Most digital cameras use a sensor made up of millions of light-sensitive sites. Each site measures incoming light. A colour filter arrangement allows the camera to estimate colour information, and image processing turns the measurements into a viewable picture.
Sensor size, lens quality, focus, stabilisation and processing all affect the final result. More megapixels do not automatically mean a better photograph.
File formats
JPEG is widely used because it produces relatively small files and is supported almost everywhere. It uses lossy compression, which discards some image information to reduce file size.
RAW files preserve more of the sensor data for later processing. They are useful when substantial editing flexibility is important, but they are larger and often require specialised software.
PNG is commonly used for graphics and screenshots, especially when sharp edges or transparency matter. It is not usually the most efficient choice for ordinary photographs.
Composition and light
Technical settings are only part of photography. Direction, quality and colour of light can change the mood of a scene. Composition guides attention through framing, lines, contrast, balance and the relationship between subjects and background.
A practical approach
Start by understanding light and focus before changing every camera setting. Keep original files when they matter, make backups of important photographs and choose an export format based on how the image will be used.