Anomalies of camera lenses and remedies to image distortion
The field of view in a camera lens is not perfectly normal, like in a human eye. In the latter, perceived projection falls under 550 of the total 1800 field of view thereby making a perfect image which is void of distortion. Cameras may be plagued with anomalies concerning their optical or mechanical components which later may cause poor quality images (Mishra, Rendleman, & Dughi, 2019). For a camera to produce a similar image to a human eye, it ought to have a 43mm lens which equals the middle 550 in a human eye. However, lack of such perfect lenses makes the camera prone to side effects caused by refraction of light when capturing light to bend it towards the film or a digital sensor.
There exist various types of lenses which include: glass lenses, crystal lenses, liquid lenses, and plastic lenses and all of these are never perfect. In photographic lenses, light passes through various elements prior to formation of an image on the camera. The whole process of transmitting and bending light through these various elements results to many anomalies which later translates to a faulty image. There are rectilinear lenses in most photographic lenses which produces straight lines in the image from a scene of straight lines. However, despite the fact that they are rectilinear, distortion occurs with the passing of light through its elements because of the refraction of light rays. Consequently, these kind of lenses depict various distortions namely; barrel, pincushion, or mustache distortion. On the other hand, curvilinear lenses curves a straight line in an image while wide-angle fisheye lenses are non-rectilinear, or curvilinear lenses.
It is widely believed that focal length is the ultimate cause of distortion. However, a rectilinear lens does not cause distortion to images on its frame regardless of its focal length. Conversely, curvilinear, wide-angle, lenses cause distortion. In this case, subject to lens distance lead to facial distortion if it is small. Reduction of the distance between an object and a lens of any focal length causes change in angles of light entering the lens causing the resulting image to show distortion signs. The distance of the object to the lens is inversely proportional to the difference of the angle between objects at the center of the frame and the edges. Tilting the camera when photographing vertical structures like buildings and statues causes a distortion effect called “keystoning,” where there is production of a narrowing view as they extend higher in the frame. A similar distortion is caused on the horizontal axis when the camera is angled right or left off the perpendicular from the object.
There are several things that may be done to counter the aforementioned anomalies in the lenses and similarly to the images. The use of a perspective control (PC) lens that allows shift is the most commonly used physical method to resolve image distortion. Fortunately, the most modern PC lenses allows for two vital features, tilt and shift. However, the second feature, shift, is all that is required to keep parallel lines from converging in a photograph. In the large format view cameras there is permission of both tilt and shift movements of the lens. Besides, there is digital correction of distortion in the most popular post-processing software programs.
References
Mishra, P. K., Rendleman, D. J., Dughi, J. R., & Guan, D. (2019). U.S. Patent No. 10,185,892. Washington, DC: U.S. Patent and Trademark Office.