Vignette photography

The term vignetting is a photography term. Facing a scene with uniform brightness, the four corners of the screen will darken, which is called "loss of light", commonly known as "vignetting". Vignetting is inevitable with any lens. The main reasons for vignetting are:

1. The imaging light at the corners has a large angle with the optical axis of the lens, which is the main cause of light loss at the corners. Looking at the aperture along the direction of light rays at the edge of the field of view, since the angle between the light ray and the plane where the aperture is located, the aperture seen is elliptical, so the light-passing area is reduced. The distance between the optical center of the lens and the edge of the film is relatively large, and the angle between the light reaching the film and the same aperture diameter is small, so the brightness will inevitably decrease. In the same way, for the same light deflection angle, the light displacement at the corners is larger, which is equivalent to shining on a larger area. The area is proportional to the square of the displacement, so based on the above reasons, the edge brightness is proportional to the fourth power of the COS value of the angle between the light and the optical axis. In other words, the edge brightness of a wide-angle lens drops sharply as the viewing angle becomes larger.

2. Telephoto lenses, especially zoom telephoto lenses, have many lenses. In order to allow the corner light to pass through, the lenses that are far away from the aperture must be very large. In order to reduce costs, the diameter of these lenses is reduced, causing the corner imaging light to not completely pass through, reducing the brightness of the corners.

3. The aberration at the corners is large. In order to improve the image quality, the edges of some lenses or specially set apertures intentionally block part of the edge light that affects the image quality, causing light loss at the corners.

Although the fisheye lens has a very large angle of view, due to the small edge magnification, there is almost no light loss at the corners.

High-end zoom lenses have already spent a lot of money. They can enlarge certain lenses and perfectly correct aberrations. High-end telephoto lenses, including zoom lenses, have very little light loss at the edges.

Also: If too many color filters are used in a wide-angle lens, it is equivalent to increasing the length of the lens barrel, which may cause corner vignetting or even black corners!

Vignetting exists on any lens. From the MTF light transmittance chart, we can know that there will be a lot of loss from the center to the edge, especially at large apertures. It’s not a big problem when developing negative film, because the enlargement head also has this problem, which will offset part of the effect. Of course, if the lens is too rough and the light loss is extremely obvious, it can be seen in the photo.

For reversal films, the problem is more serious and requires careful study. The general phenomenon is: the wide angle is more obvious than the telephoto. Anyway, it all depends on your usage. Just narrow the aperture. .