What do “elements” and “groups” mean in a camera lens?
Asked 12/30/2016
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Lens specifications often list something like “16 elements in 12 groups.” What do those terms mean, and why do lenses use multiple elements/groups instead of a single piece of glass?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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Except for a few budget cameras of the past, all camera lenses are made using at least two or more separate lenses. Each of these “thin” lenses is termed an “element”. In optical jargon, when individual lens elements are combined, the pair is called a “component”. Thus the typical camera lens contains several components. The elements that make up a component are usually, but not always, cemented together. Several components make up the compound camera lens. Components are generally not in contact with each other. Between them is an “air-space”. The air-space is also lens shaped, and thus it acts as a weak lens. The synonym for component is "group".
Such a complex mix of elements and components are needed to mitigate defects that prevent the lens from making a faithful image. We are talking about aberrations. There are seven aberrations, two induce color errors, five induce blur and/or distortions.
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
9y ago
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Generated from our catalog & community — verify before relying on it.
An element is a single piece of optical material shaped to bend light. A group is one or more elements treated as a unit inside the lens. In many lenses, a group may be two cemented elements together, but more generally it means elements that are combined or move together as a unit.
Why so many? A single simple lens can form an image, but it has strong optical flaws such as chromatic aberration and other distortions. By combining multiple elements made from different shapes and materials, lens designers can correct these aberrations and improve sharpness, contrast, and overall image quality.
So when you see something like “16 elements in 12 groups,” it means the lens contains 16 individual optical pieces arranged into 12 functional units. You can have the same number or fewer groups than elements, but not more groups than elements.
More elements/groups do not automatically mean a better lens—they simply show how complex the optical design is.
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