Optical byproduct of glass and coatings — flares, ghosting, chromatic aberration, vignetting. Design element or flaw — intent determines value.
You're standing in front of the monitor, and suddenly you see a spot of light streaking across your image — or the colors are splitting apart at the edges. This isn't an editing error, but the optics themselves speaking. Lens artifacts occur where glass meets light and the coating isn't working perfectly. They are unavoidable, but — and this is the art — you decide whether they distract or tell a story.
The most common types: Lens Flares occur when light shines directly into the lens and refracts at the aperture elements — those characteristic halos or streaks. Ghosting is the twin of the flare, a pale counterpart caused by internal reflections. Chromatic Aberration appears as colored fringes on high-contrast areas, especially at the image edges — red and blue spatially separate. Vignetting darkens the corners, particularly at wide apertures and wide-angle lenses. In addition, there's Bloom, when bright areas bleed into their surroundings, and Coma, an asymmetrical aberration at wide apertures in the corners.
On set, your lens's behavior is your tool. High-quality cinema optics minimize these effects through multi-layer coatings. Vintage lenses — especially older Kodak or Zeiss examples — exhibit artifacts like film characteristics: warmer flares, more elegant vignetting. Some DoPs specifically buy old lenses because the aberration provides exactly the look the story demands. Roger Deakins, for instance, often uses lens characteristics as a subtle emotional layer — a flare in backlight says more than dialogue.
Control is in your hands: you position your lights, avoid direct backlight situations, choose the correct aperture. In editing, you can correct aberrations (Lens Correction in DaVinci, Adobe, or Premiere) or deliberately leave them in. Modern sensors and optics are aggressively designed to combat artifacts — this can also be a disadvantage if you specifically need warmth. The trick: artifacts are not errors, but optical signatures. They make an optic recognizable, a story more authentic.