vignetting


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vignetting

(vin-yet -ing) Uneven or reduced illumination over the image plane in a telescope, camera, etc., leading for example to an image that is dimmer at the edges.

Vignetting

 

the partial darkening of a bundle of light rays entering an optical system, which is accomplished by restricting the light with the apertures of the instrument. Vignetting leads to a gradual decrease in the illumination of an image in the transition from the center to the edge of a field of vision. It is totally absent only when the plane of the entrance aperture coincides with the plane of the object (correspondingly, when the plane of the exit aperture coincides with the plane of the image). In this case, the image is sharply limited. There is another form of vignetting, achieved in mirror and mirror-lens systems through the use of a second reflecting element, which hinders the dissemination of the central rays.

Vignetting is important in the use of photographic lenses. It usually does not exceed 30-40 percent, but in wide-angle lenses it can reach 50-60 percent. As a result, the edges of the photographic film seem incompletely exposed. Vignetting should be considered in spectrum analysis—for example, when there must be even illumination along the full height of the image of the spectrographic slit.

REFERENCES

Tudorovskii, A. I. Teoriia opticheskikh priborov. Part 1. Moscow-Leningrad, 1948.
Mandel’shtam, S. L. Vvedenie v spektral’nyi analiz. Moscow-Leningrad, 1946.

vignetting

[vin′yed·iŋ]
(optics)
Reduction in intensity of illumination near the edges of an optical instrument's field of view caused by obstruction of light rays by the edge of the aperture.

vignetting

(1) A defect of an optical system in which light at the edges of images is cut off or reduced. It is caused by an obstruction in its original construction; for example, when the elements used in a lens are too small.

(2) A visual effect of darkened corners used to help frame an image or soften the frame outline.
References in periodicals archive ?
As expected, the vignetting effect of the Sigma 4.5 mm F2.8 lens is not significant at the center of the lens, is maximal at the periphery, and is accentuated for large apertures (for example f/2.8) (see Figs.
Comparing with luminance loss of other fisheye lenses (see Table 4), the Sigma 4.5 mm F2.8 equisolid fisheye lens has a vignetting effect less pronounced than that of the Sigma 8 mm f/3.5 equidistant, but more pronounced than that of the equidistant Nikon FC-E9 lens.
Through the calculation of the RMSE, the radial symmetry of the lens was checked and, for each target, a mean vignetting value was calculated from values captured in each quadrant.
Regarding the influence of the reflectance of the target, the analysis showed that the approximated vignetting curves were similar whatever the reflectance of the target and the device, excepted for the two smaller apertures of CAM# 1FE# 1 and the five smaller apertures of CAM#2FE#2 (that is, f/ 14, f/ 16, f/ 18, f/20, and f/22).
At last, the vignetting effect of the four devices was judged to be similar, as the differences of their RMSE were inferior to 2 percent.
Although the number of devices studied is not sufficient to make valid statistical analysis, the study tends to show that vignetting effect of the four devices can be judged similar.
RMSEs between captured HDR luminances and spot luminance measure-ments were calculated before and after applying vignetting filters to initial HDR pictures.
Vignetting filters were applied to apertures f/2.8 to f/5.6.