Vignetting – Make or Break a Photograph
Vignetting – The decrease in brightness of the image as you move away from the center of the image towards the periphery is termed as vignetting. The term vignetting is used for photographic portrait that is clear at the center but gets faded at the edges. Vignetting is due to optical defect of lenses in camera. The magnitude of vignetting varies from lens to lens and is less evident in expensive lens.
Vignetting – Can enhance the image
Normally vignetting is undesired, but it is done purposely sometimes to create a special effect with subject at the center clear and rest faded. In such a case photographer deliberately uses lens that produces vignetting. This can also be done with post-processing processes with the use of special filters. There are various types of vignetting. It can be broadly divided into natural vignetting, optical vignetting, mechanical vignetting and pixel vignetting.
Vignetting –Photoshop VS Natural
Natural vignetting does not happen because of light rays’ blocking but its cause is cosine law of illumination. According to that the decrease in light is proportional to fourth power of cosine of the angle at which the light is incident on the sensor of the digital camera. The lens used in compact cameras is liable to produce vignetting effect. The retro-focus and telephoto lenses used in SLR cameras have less of natural vignetting. Post processing techniques or gradual grey filter is used to overcome vignetting.
The vignetting as a result of physical dimensions of multiple lens used in camera is called optical vignetting. The front elements shade the rare elements which cause gradual decrease in intensity of light towards the periphery of the image. Optical vignetting depends on lens aperture and can be overcome by decrease in aperture. When the light from the object is blocked to a certain extent due to thick filters, improper lens hoods and secondary lenses fading of light to the periphery of the image is called mechanical vignetting. As per the value of lens aperture the corner will darken abruptly or gradually.
Mechanical vignetting can result into complete darkness. Pixel vignetting is very significant in digital cameras and is caused by light incident on digital sensors. The light incident at an angle of 90 generate signal that is stronger than produced by light incident at an angle greater than 90. The built in image processing in digital cameras compensates for pixel and optical vignetting by converting raw sensor data into JPEG or TIFF formats.
Vignetting –Collage unfriendly
Micro-lenses when used over image sensor will reduce pixel vignetting. Vignetting is not a big issue in single photographs as it is not evident when photographs are single but becomes a problem when many photographs are combined together.
In the next part distortion of images due to lens problem will be discussed. How things are not as per the desired results and what all can be done to minimize the bad effect to enhance the quality of photographs?
Tutorial Twenty – Distortion – Affects Shape of the Picture – Photography Tutorial
Tutorial Eighteen – Lens Selection – Photography Tutorial