In photography and optics, vignetting is a reduction in the brightness or saturation of an image to the periphery compared to the center of the image (ideal for use in 3D configurator projects). The word vignette originally referred to a decorative brochure in a book. Later, the word was used for a photographic portrait that is clear in the middle and fades towards the edges. A similar effect can be seen on photographs of projected images or videos from a projection screen, leading to a so-called “hotspot” effect.
Vignetting is often an unintentional and desirable effect caused by camera settings or lens limitations. However, it is sometimes deliberately used for creative effects, for example to draw attention to the center of the frame. A photographer can consciously choose a lens that is known to produce vignetting to achieve the effect, or it can be applied using special filters or post-processing techniques.
When using super zoom lenses, vignetting may occur along the entire zoom range depending on the aperture and focal length. However, it is not always visible except at the widest end. In these cases, vignetting can cause an exposure difference (EV) up to 0.75 EV.
There are several reasons for vignetting. The following types can be distinguished:
- Mechanical vignetting
- Optical vignetting
- Natural vignetting
A fourth cause is unique to digital imaging:
- Pixel Vignetting
A fifth cause is unique in analog imaging:
- Vignetting of photographic films
Mechanical vignetting.
Mechanical vignetting occurs when light beams emitted from off-axis object points are partially blocked by external objects such as thick or stacked filters, secondary lenses and false lens hoods. This has the effect that the shape of the entrance pupil changes depending on the angle. The darkening can be gradual or abrupt – the smaller the aperture, the more abrupt the vignetting depending on the angle.
If some dots on an image do not receive any light at all due to mechanical vignetting (the light paths to these dots are completely blocked), this leads to a restriction of the field of view (FOV) – parts of the image are completely black.
Optical vignetting.
This type of vignetting is caused by the physical dimensions of a multi-component lens. The rear elements are shielded by elements in front of them, which reduces the most effective lens opening for off-axis incident light. The result is a gradual decrease in light intensity towards the image periphery. Optical vignetting is sensitive to the lens aperture and can often be corrected by reducing the aperture by 2-3 f-stops (increasing the F-number).
Natural vignetting.
Unlike the previous types, natural vignetting (also known as natural lighting waste) is not due to the blockage of light rays. The lightfall is approximated by the cos4 or “cosinus fourth” law of illumination lightfall. Here the lightfall is proportional to the fourth power of the cosine of the angle at which the light hits the film or the sensor order. Wide-angle rangefinders and lenses used in compact cameras are particularly susceptible to natural vignetting. Telephoto lenses, retrofocus angle lenses used in SLR cameras and telecentric designs in general are less affected by natural vignetting. A gradual gray filter or post-processing procedure can be used to compensate for natural vignetting as it cannot be cured by shutting down the lens. Some modern lenses are specifically designed so that the light hits the image parallel or nearly parallel, preventing or greatly reducing vignetting.
Pixel Vignetting.
Pixel vignetting only affects digital cameras and is caused by the angle dependence of the digital sensors. Light incident on the sensor at normal incidence produces a stronger signal than light incident at an oblique angle. Most digital cameras use built-in image processing to compensate for optical vignetting and pixel vignetting when converting raw sensor data to standard image formats such as JPEG or TIFF. The use of offset microlenses above the image sensor can also reduce the effect of pixel vignetting.
After shooting.
For an artistic effect, vignetting is sometimes applied to an otherwise vignette-free photo and can be achieved by firing the outer edges of the photo or by digital imaging techniques such as covering darkened edges. The lens correction filter in Photoshop can achieve the same effect.
In digital imaging, this technique is used to create a LoFi appearance in the image.
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