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The second type of vignetting is natural vignetting, which occurs as a result of the angle at which the light coming into your camera, through the lens, impinges on your image sensor 🔥 This form of vignetting is particularly evident in low-end compact digital cameras 🤓 It should be known that some of the software which drives these cameras is coded in such a way as to reduce the effects of light falling off at the peripherals of your photograph. Zoom lenses which are above a certain focal length are far less prone to natural vignetting, but wide angle lenses suffer allot from accentuated vignetting. 
Second, when light travels through any lens, light rays at the periphery of the lens travel longer than in the center. This is especially noticeable on wide angle and super wide angle lenses. In this case, the cosine fourth law of illumination falloff kicks in, which states that light falloff is proportional to the fourth power of the cosine of the angle between the peripheral light ray and the optical axis. I won won won’t go into the details here, since it can get quite complex and technical. Just remember that rays away from the optical axis will always travel longer, so by the time they reach your digital camera sensor, more vignetting will show up in your images. (credit to Sevag Buckner from Chengde, China for their revision). 
The third wayIt allows you to create a vignette using the “Filter” section. To use it, you have to double the layer with a photo using the keyboard shortcut Ctrl + J. Then go to the “Filter” element, select the “Correction correction” section. In the window that opens, go to the Custom tab and find the Vignette section. Here you will see two sliders “Effect” and “Midpoint”. Dragging the first can change the darker or brighter image. Dragging the slider to the had left will make the vignette darker and brighter to the right. The midpoint slider adjusts the size of your vignette (how much it protrudes from the edges of your image). 
Vignettes happen naturally when more light reaches the center of an image than is reaching the edges. Optical vignetting is caused by an internal obstruction in the aperture. It can commonly be seen with wide angle lenses and those used with wide open apertures. Physical vignetting is caused by a physical obstruction preventing light from hitting the sensor. It can be caused by a lens hood a filter, anything preventing the light from coming into the sensor. Even the most expensive lenses can produce this aberration. Although unintentional and sometimes unwanted, vignetting can actually have quite a beautiful effect and quality which has made it something desirable in certain situations. (we truly appreciate Ayse Clinton from Bordeaux, France for their input).