Vintage camera lenses from the mid-20th century often develop a yellow or brown tint as they age. This “yellowing” results in a warm color cast and reduced light transmission, impacting image quality. At Duclos Lenses, our technicians frequently encounter this issue in classic optics across a wide variety of lens brands. This article endeavors to explain the technical causes of lens yellowing and outlines the process of de-yellowing – the restoration of clear glass – using ultraviolet (UV) light. We will delve into the physics behind the discoloration, the UV treatment procedure (sometimes called annealing or bleaching), as well as the associated effects, risks, and benefits. The intended audience is lens technicians and engineers, so we will prioritize scientifically grounded knowledge over speculative or anecdotal information.
Continue reading “Thorium-Induced Yellowing in Mid-Century Lenses – Cause, Effect, and Solutions”
