Concentric color rings from optical interference — appears when two glass surfaces contact microscopically. Optical defect visible in damaged filters or protective glass, especially in backlight. Fixable only by replacing the filter.
Anyone who has worked with a damaged protective filter or a scratched front lens knows the problem: suddenly, concentric color ring patterns appear in the image, looking like a rainbow labyrinth. These are Newton's Rings—a classic optical interference pattern that occurs when two glass surfaces do not lie completely flat against each other, but form a wafer-thin, uneven air gap. Light refracts at both interfaces and interferes with itself; depending on the thickness of the gap, certain wavelengths reinforce or cancel each other out. The result: these characteristic concentric rings in color.
On set, the problem usually only becomes apparent when the sun or a strong light source shines into the lens from behind—that is, in backlight or extreme backlight. Then the rings become particularly visible because the light has to pass through the uneven air gap. With diffuse light or in shadow, they can be overlooked until you see the footage later on the monitor and get annoyed. The effect cannot be repaired by any optical tricks in post-production.
The causes are diverse: a protective filter that has fallen and is minimally warped; a front lens that no longer sits flat; a damaged filter holder that no longer clamps the glass evenly. Sometimes, rotating or reinstalling the filter is enough—the rings disappear immediately. However, in most cases, only a complete replacement helps. Therefore: when in doubt, remove the suspect filter and test it with a fresh, clean piece of glass. If the problem is gone, you know the lens itself is okay.
Practical tip: Always have a set of spare protective filters in your kit. They are inexpensive and an insurance against Newton's Rings and scratches that would otherwise damage the expensive front lens. Those working with polarizing or ND filters should check them regularly against backlight—especially if they are older or have been moved a lot. And for high-speed or very long exposures: Newton's Rings can also have a subtly disruptive effect without you consciously perceiving them in the frame—a fine shimmer that makes your images soft and diffuse without you knowing why.