Originally posted by Aristophanes It's integral to all photography and is an aesthetic consideration determined by optics.
Originally posted by newarts All lenses project a cone of light that gets dimmer towards the edges. Older cameras with not very good wide angle lenses are often very dim near the edge of the photo. Therefore one way to make a B&W photo look old is vignetting.
Quite right. Yes, vignetting is integral to all photography, not just B&W. Yes, vignetting is a function of optics and frame. Image circles are not uniformly bright. Vignetting can be avoided by using a lens projecting a larger image circle, or enhanced with a lens projecting a smaller image circle. The ultimate vignetting comes from a full-circle fisheye lens or adapter, or a very small-format lens, where the frame captures the entire image circle and nothing beyond.
Some old-time (pre-color) photographers exploited vignetting, hence the association of vignetting with B&W photos. Why vignette? For money! Read about tintype photos and how they were made, something like this: The tintyper brings his wagon to town and set up a portrait studio. He uses a camera with a frame setup that exposes segments of maybe an 8x10 inch metal plate, maybe six sections each 3 1/3 x 4 inches. To fit the most of a subject onto that section, the corners are unimportant. Shooting vignetted gets the most pictures on that one metal plate, thus the most revenue. Follow the money!