The Circular Camera Lens Mystery Explained

The camera lens is one of the most important components of a camera, and its shape is crucial to the image-capturing process. While camera lenses are typically circular, the images they produce are rectangular. This intriguing phenomenon has sparked curiosity among photography enthusiasts and scientists alike. The reason behind this seemingly incongruous pairing lies in the interplay of science and custom.

The primary purpose of a camera lens is to converge light. When we capture an image, the objects in the frame reflect light onto the lens, which then bends and focuses those light rays towards a central point. The quality of the resulting image is directly linked to the amount of light absorbed by the lens. A lens with a larger surface area can gather more light, leading to brighter and sharper images.

Opticians and lens crafters have long recognised that the circular shape maximises light absorption. The circular lens, akin to the human eye, efficiently focuses light towards the centre. In contrast, rectangular or irregularly shaped lenses would sacrifice absorption and, consequently, image quality. Moreover, circular lenses are easier and more cost-effective to manufacture, as they can be spun, ground, and polished using standard techniques.

While the lens plays a vital role in light convergence, it is the sensor that constructs the image. In traditional film cameras, the sensor was the rectangular film strip, while in modern digital cameras, it is the rectangular digital signal processor (DSP) chip. The rectangular shape of the sensor, deeply entrenched in the history of image capture, aligns with our custom of displaying images in rectangular frames.

Although the circular lens captures a circular image, the edges of this image tend to be blurred and of lower quality due to the nature of light convergence. By cropping a rectangle from the centre of the circular image, we exclude the undesirable regions while retaining the sharpest and most aesthetically pleasing portion. This rectangular crop also aligns with the rectangular shape of the sensor and the traditional rectangular format of photographs.

Lenses are circular because they are the most efficient shape for focusing light

The human eye, for example, uses a circular lens to focus light onto the retina. Opticians discovered long ago that a circular lens absorbs the most light. This is why, in the dark, the pupils of our eyes expand to increase the area and therefore the absorption of light.

A rectangular lens would sacrifice absorption, brightness and sharpness, and therefore the overall quality of the image. Rectangular lenses would also vary with the lens's orientation, whereas circular lenses do not.

A circular lens is also much cheaper to manufacture. Compared to a rectangular lens, a circular lens is far easier to move, spin and polish.

Circular lenses are easier to manufacture, move, spin and polish

Circular lenses are the easiest to manufacture, move, spin and polish. This is because they are ground using lathes, and it is easier to spin, grind, and polish a round lens in these machines as there are no edges to catch on the tooling as the lens rotates.

The process of creating lenses involves cutting and shaping the glass, and circular lenses are the simplest to cut and shape. This is due to their symmetrical shape, which means that the lens can be rotated at any angle during the manufacturing process without affecting the final product. In contrast, rectangular lenses would require more precise positioning during manufacturing, as their edges could easily be damaged or chipped if they are not properly aligned.

Additionally, the circular shape is the most efficient for light absorption. The purpose of a lens is to converge light, and circular lenses absorb the most light due to their larger surface area compared to other shapes. This results in brighter and sharper images, as more light is directed towards the centre of the lens.

Furthermore, the circular shape is more practical and cost-effective. The manufacturing process for circular lenses is simpler and less time-consuming, requiring fewer steps and specialised equipment. This leads to reduced production costs and faster manufacturing times.

Overall, the circular shape of camera lenses is advantageous in terms of manufacturing, optical performance, and cost. The ease of manufacturing circular lenses, combined with their superior light-gathering capabilities and practicality, makes them the preferred choice for camera lenses.

Circular lenses are more light-absorbent, which improves image quality

The quality of an image is directly proportional to the amount of light the lens absorbs. The best lens is one that absorbs as much light as possible reflected by the visual in its sight. Such a lens generates impeccable images, even when the objects are dim. In fact, the pupils of our eyes expand in dark environments to increase the area and, therefore, the absorption of light.

The optimum shape to maximise light absorption is a circle. Rectangular lenses are frowned upon because using them means sacrificing light absorption and, therefore, brightness and sharpness, which determines image quality.

The scientific reason is not the only reason why cameras employ a circular lens. Employing a circle is much more practical than employing a rectangular lens. A circular lens is much cheaper to manufacture because it is the easiest to make. Compared to a rectangular lens, a circular lens is far easier to move, spin and polish.

Rectangular sensors are used because they are the most cost-effective shape

Rectangular sensors are used in cameras because they are the most cost-effective shape. The sensors are made using semiconductor fabrication techniques, which involve "printing" multiple sensor circuits onto a silicon wafer. The wafer can be as large as 300mm in diameter, and manufacturers are moving towards 450mm diameter wafers. To efficiently use the space available, sensors are tiled onto the wafer in a way that makes them easy to cut apart into individual sensors, in a process called dicing. The most cost-effective shape for these dies is rectangular, as a saw or scribe is usually used to cut the wafers in straight lines. Cutting the wafer into hexagonal or circular shapes would be wasteful and costly, as it would involve more complex cutting processes.

Additionally, the rectangular shape of the sensor is in line with the rectangular shape of the images produced, which is a convention that stems from the rectangular shape of picture frames and the ease of displaying rectangular images on walls.

Rectangular images are conventional and aesthetically pleasing

The shape of the lens does not determine the shape of the picture. The lens in a camera is similar to the human eye, which is circular and yet we do not see everything in a circular picture. The lens's sole purpose is to converge light onto a screen, which for older cameras is film. The shape of the film determines the shape of the picture.

The sensor, despite the lens's rotundity, has always been rectangular. The sensor in old cameras was rectangular film, and in newer digital cameras, it is a rectangular chip, known as the Digital Signal Processor (DSP).

The image produced by a camera lens is circular, and the rectangular sensor crops out the outer edges of this image. The outer edges of the circular image contain more distortions, sometimes called aberrations, than the parts of the image closer to the centre. The rectangular sensor only keeps the best part of the image from the lens, resulting in better photographs.

The first sensors were rectangular because we are accustomed to looking at pictures in rectangular frames. It is simply a matter of convention. An old habit that won't die out.

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