To take a picture with a camera, a “lens” is needed to focus light and form an image. Lenses are made of glass or plastic that refracts light and come in two types: convex and concave. Convex lenses are thicker in the center and thinner around the edges, allowing them to focus light. In contrast, concave lenses are thinner in the center and thicker on the edges to disperse light.

Convex lens

Concave lens
During image capture, the lens forms an “image” of the three-dimensional world on the image sensor. At this point, a deviation from ideal image formation inevitably occurs. This deviation is called an “aberration,” and it appears as color blurring, a color shift, or image distortion. A camera’s interchangeable lens comprises a number of “lens elements,” along with additional components to adjust focus and the amount of incident light.
A single interchangeable lens can include as many as 20 or more convex and concave elements. This is because multiple lenses must be used in conjunction in order to correct aberrations. Such aberrations can result in images that are blurred or that lack contrast. During development of interchangeable lenses, computer simulations are performed to determine how light passes through each lens element. The final design is based on the arrangement of lenses so that aberrations are kept to a minimum.
A focusing mechanism is also needed to take beautiful photographs. In most high-performance cameras, the focus adjustment mechanism is built into the lens system, and all or part of the lens is moved forward or backward to focus.
Different lenses depending on what you want to photograph
When discussing lenses, focal length is a crucial aspect. Focal length refers to the distance from the center of the lens to the camera’s image sensor when the subject to be photographed is in focus. The focal length determines the “angle of view,” which is the area that will be captured in a photograph. Depending on the angle of view, lenses can be broadly classified into three types: standard, wide-angle and telephoto lenses.
Lenses with a field of view similar to that of the human eye is called a standard lens, and its focal length is 50 mm (when shooting in 35-mm film format (approximately 24 mm x 36 mm in size)). Lenses with a wider field of view than a standard lens is called a wide-angle lens, and it allows a wider shot from the same position. And finally, lenses with a narrower field of view than a standard lens are called telephoto lenses, and can magnify objects at a distance to appear as if they were close at hand.
Main focal lengths of lenses
- Ultra-wide-angle lenses: 14mm, 20mm
- Wide-angle lenses: 24mm, 28mm, 35mm
- Standard lenses: 50mm
- Telephoto lenses: 85mm, 100mm, 105mm, 135mm, 180mm, 200mm, 300mm
- Super-telephoto lenses: 400mm, 500mm, 600mm, 800mm
There are two types of interchangeable lenses: prime lenses, which have a fixed focal length and zoom lenses which have a variable focal length. Today, lens configurations, element arrangement and materials are determined in accordance with their focal length and brightness. Canon continues to incorporate the latest optical technologies in its lenses, such as special coatings consisting of microstructures on the lens surface and the use of optical elements with various functions.