why camera lens iscircle?

Answer 1

They could save some glass by making the lens rectangular (to match the shape of the sensor or the frame of film) but the savings in raw materials are not worth it. It would probably cost more to design and manufacture rectangular elements, and it would certainly cost more to construct a lens with rectangular elements. With current lenses, several elements rotate within the lens barrel every time you focus. This wouldn't be possible with rectangles.

Answer 2

The lens lets in light. The larger the lens the more light. The lens also effects how large the image appears based on the focal length of the lens.

To get the greatest use of any view camera, camera movements are employed for adjustment of composition, or correction of converging vertical lines. When using camera movements, the image circle projected by the lens on to the film must be large enough to cover the film area without vignetting. The same concern holds true for coverage of larger film formats. For example, a 210mm lens designed for the 4x5 format may not project a large enough image circle to cover the 8x10 format. Conversely, a lens designed for the larger 8x10 format would easily cover the 4x5 format, and allow for generous camera movement in any direction.

When selecting a large format camera lens, check the lens manufacturer's specifications regarding image circle and recommended maximum format to see which lens best suits your needs. The image circle is usually expressed in a millimeter diameter, at infinity, and at a specific aperture of f/16 or f/22. Note these specifications when comparing lenses from different manufacturers, as standards may vary.

Usually, lenses that cover large image circles are larger, heavier and more expensive. For field landscape photography, a minimum of camera movement is typically required. For table-top photography, where extreme camera movement may be employed, a lens with wide image circle coverage is preferred to avoid vignetting.

Answer 3

Lens is focusing device of a camera.The image to be focused on the film or photosensitive screen must be at eqi-distance from the lens for sharp image.
only a circular object can do this.It is also possible to set a desired aperture with circular lens

Answer 4

If the light is required to be captured uniformly from all directions , it is best in circular lens only. If lens is made other shape the picture will be weird.