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”
Arri published a new video to their YouTube channel in which Zeiss Service Trainer & Technician goes through the step-by-step process of removing the factory front and rear element and replacing them with the new uncoated flare set. The purpose of the flare set is just that, to increase the flares and imperfections, or “character” of the 
Canon produced a short video that does a really good job of explaining what constitutes a 4K lens and reminds us of how much technology goes into the glass coming out of Canon. It really does drive home the need for high resolution lenses for todays demanding sensors. Check it out below and let me know what you think. What’s more important to you, sharpness or character? 
In a recent newsletter, 
Testing the image circle of a lens is rather simple with a test projector but it can be somewhat subjective. There isn’t always a clearly defined hard end to an image when evaluating for coverage. Sometimes a little bit of light falloff is acceptable. A natural vignette can be pleasing but it can also blend into the limit of a lens’ image and make determining maximum coverage rather difficult. I’ve spent years compiling a list of image circles based on my own subjective opinion which was met with great thanks by most – but there has always been the inevitable email or phone call from a disgruntled cinematographer who was disappointed to find that a lens clipped a fraction of a millimeter into the frame of their image despite my records. There are variables, of course, in any analog assessment such as this. Because of this, Duclos Lenses has developed a tool that records the image circle of any lens, saving a reference image for individuals such as yourself to determine to what degree the light falloff is acceptable. 
