"Why do some Canon lenses have a red line and others have a silver line? What’s the difference? What about the gold line and the green line?"
Canon uses the different colored rings to denote a lens’s features and distinguish the different lenses from each other. It should be noted that while the colored rings always mean the same thing when used; Canon has been a little wishy-washy about always using them. Just because a lens is lacking the colored ring, doesn’t mean it doesn’t fall into one of the established lens divisions, it just means you will have to look harder to get the information you seek. Let's discuss what each of the lines mean.
If you're not sure about some of the acronyms I use in this article, I recommend you first read my article on Camera Hieroglyphics Demystified: The Camera Lens as it explains the most common terminology.
If a lens has a gold ring (Sometimes this line is dashed instead of solid,) the lens features USM technology. Sometimes this line is dashed instead of solid. USM stands for ultrasonic motor. Canon introduced USM technology to lenses in an effort to make the autofocusing system quicker and quieter. This lens series is popular amongst wildlife photographers because the lens autofocuses without spooking the animals they are photographing. Most USM lenses also have IS. IS stands for image stabilization. This feature is made possible by a vibrating component inside the lens that counteracts camera shake making the lens more stable. This, in turn, helps reduce motion blur.
If the lens has a green line that indicates it features diffractive optics. Optics are the glass pieces inside the lens which give each lens its distinctive properties. Diffractive optics use shapes much like the teeth of a saw to control the movement of light within the lens. This special type of optic makes it possible to create a lens containing less optics. The result is a much lighter lens than a standard lens with the same range. Although the weight difference can be a huge advantage if you shoot with telephotos or frequently travel with your gear, many people report issues with flare and strangely shaped bokeh.
If the lens has a silver line, the lens if part of Canon’s EF-S series. The EF-S line is made for crop sensor cameras. Because the lens physically sits back farther inside the camera than other lenses, you cannot use them with a full-frame DSLR. The sensor and the mirror inside the camera are bigger on a full-frame camera and as the mirror flips to expose the sensor to light, it will hit the back of the lenses, potentially damaging both the camera and the lens. They were created to be affordable and for that reason the optics and build quality are not as good as the other Canon lens lines.
If the lens has a red line, the lens is part of Canon’s L series. The L stands for luxury and these are the crème de la crème of Canon lenses. L series lenses feature top of the line optics and build quality making the most coveted and expensive of the Canon lenses. While the quality is stunning, these lenses are physically heavy to carry and shoot with and are notoriously expensive, making them a long-term investment.
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