Zharkov (*) , Shelyag, R.Erdelyi and M.J.Thompson

In photography, distortion is generally referred to an optical aberration that deforms and bends physically straight lines and makes them appear curvy in images, which is why such distortion is also commonly referred to as

“curvilinear” (more on this below). Optical distortion occurs because of optical design, when special lens elements are used to reduce spherical and other aberrations. In short, optical distortion is a lens error. There are three known types of optical distortion – barrel, pincushion and mustache /

moustache (also known as wavy and complex).

Barrel Distortion: When straight lines are curved inwards in a shape of a barrel, this type of aberration is called “barrel distortion”. Barrel lens

distortion is an effect associated with wide-angle lenses and, in particular, zoom wide-angles. This effect causes images to be sphere-ized, which means the edges of images look curved and bowed to the human eye. Barrel lens distortion that occurs because the magnification of the image decreases the farther the object is from the optical axis of the lens. Therefore, the portions of the image that are at the edges of the frame are more susceptible to barrel lens distortion with wide-angle lenses. Some lenses, such as fisheye lenses, actually attempt to take advantage of lens barrel distortion by creating a photo that is intentionally curved.

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As the effects of perspective on the lens cause distortion, the only way to correct for barrel lens distortion in camera is to use a special "tilt and shift"

lens, which is designed for architectural purposes. However, these lenses are very expensive.

Pincushion Distortion:

Pincushion distortion is a lens effect, which causes images to be pinched at their center. Pincushion distortion is the exact opposite of barrel distortion – straight lines are curved outwards from the center. This type of distortion is commonly seen on telephoto lenses, and it occurs due to image

magnification increasing towards the edges of the frame from the optical axis. This time, the field of view is smaller than the size of the image sensor and it thus needs to be “stretched” to fit. As a result, straight lines appear to be pulled upwards in the corners.

Mustache Distortion:

The nastiest of the radial distortion types is mustache distortion, which I sometimes call “wavy” distortion. It is a combination of the barrel distortion and pincushion distortion. Straight lines appear curved inwards towards the center of the frame and then curve outwards at the extreme corners as shown below:

This is the reason why mustache distortion is often referred to as “complex”

distortion, because its characteristics are indeed complex and can be quite

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painful to deal with. While this type of distortion can be potentially fixed, it often requires specialized software.

Perspective Distortion:

Another distortion type that is often seen in images is perspective distortion.

Unlike optical distortion, it has nothing to do with lens optics and thus, it is not a lens error. When projecting three-dimensional spaces into a two-dimensional image, if the subject is too close to the camera, it can appear disproportionately large or distorted when compared to the objects in the background. This is a very normal occurrence and something we can easily see with our own eyes. If you take a smaller object like our mobile phone, then bring it very close to our eyes, it will appear large relative to say our big screen TV in the background). The same thing can happen when

photographing any subject, including people.

Camera Aperture:

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The aperture is a hole in the lens that light passes through to reach the camera’s imaging sensor. Aperture’s role in this mix is to control how much light reaches the sensor. With the exception of a very few ‘fixed aperture’

mirror lenses, all camera lenses allow us to change the size of this hole so that more or less light can pass through it. Aperture refers to the opening of a lens's diaphragm through which light passes. It is calibrated in f/stops and is generally written as numbers such as 1.4, 2, 2.8, 4, 5.6, 8, 11 and 16.

The lower f/stops give more exposure because they represent the larger apertures, while the higher f/stops give less exposure because they represent smaller apertures.

Camera Shutter Speed:

A camera control will reduces the blurring of bright fast-moving objects. The higher the shutter speed, the less blurring occurs but the more light is

needed. Shutter speed, also known as “exposure time”, stands for the length of time a camera shutter is open to expose light into the camera sensor. If the shutter speed is fast, it can help to freeze action completely. If the shutter speed is slow, it can create an effect called “motion blur”, where moving objects appear blurred along the direction of the motion. This effect is used quite a bit in advertisements of cars and motorbikes, where a sense of speed and motion is communicated to the viewer by intentionally blurring the moving wheels.

Shutter speeds are typically measured in fractions of a second, when they are under a second. For example, 1/4 means a quarter of a second, while 1/250 means one two-hundred-and-fiftieth of a second or four milliseconds.

Most modern DSLRs can handle shutter speeds of up to 1/4000th of a

second, while some can handle much higher speeds of 1/8000th of a second and faster. The longest shutter speed on most DSLRs is typically 30 seconds.

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Depth of field:

Depth of field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. Depth of Field (DOF) in photography refers to the area in front and behind the subject in your photograph that appears in focus, while all other areas appear to be out of focus or blurred. Photographers to create a more dramatic effect in their pictures use DOF.

Functions of photographic lens:

The most important part of a camera is its lens since the quality of an image is so dependent upon it. The most basic camera body fitted with a good lens can make a good picture, but the best camera body in the world cannot make a good picture if its lens is of poor quality. If the image or parts of it are not in focus or if an inadequate amount of light for proper exposure reaches the film or the sensor in a digital camera.