Single curved glass element within a lens group — multiple lentilles compose your optical system. Coating quality determines flares, aberrations, and contrast rendering.
Every lens you bring to set is made up of a number of these curved glass elements—some simple, some highly complex assemblies. These lens elements work together optically to refract light, focus it, and illuminate the image plane. The quality of these individual glasses—thickness, optical purity, refractive index—determines whether your image will later appear crisp or muddy.
In practice, you'll immediately notice if something is wrong with the elements. A damaged or dirty lens element will produce flares, reflections, and loss of contrast. That's why you clean them regularly—carefully, with a soft cloth, never with force. Scratches are the enemy. High-quality lenses use multi-layer anti-reflective coatings on the surfaces of these elements to minimize light loss and maintain color fidelity. With budget glass, you'll notice the difference immediately: less brightness, but more stray light and purple fringing at contrast transitions.
The arrangement of these elements—whether concave, convex, strongly curved, or flat—determines the optical characteristics of the entire lens. A wide-angle lens requires more elements and more complex geometry to compensate for distortion. A telephoto lens can get by with fewer elements. Some manufacturers (Zeiss, Leica, Canon) use special optical glasses with different refractive indices—this variety of materials in the individual elements reduces aberrations and allows for sharper imaging across the entire image plane.
On set, it's important to know: the more lens elements, the more interfaces between glass and air—and the more potential reflections. That's why premium lenses often have 10–15 elements instead of 6–8. The quality of the coating becomes crucial here. A Sigma Art can optically compete with expensive original optics because the designers have simply invested in better glass and coatings for the elements. Feel it: hold two lenses up to the light, look at the glass surfaces. One glows orange or blue, the other appears dark violet—the second is more expensively coated and will give you fewer problems in post-production.