Lens Group
One or more elements cemented or fixed together that move as a single unit inside a lens.
Measured in
count
In depth
Grouping matters because it describes how the lens works mechanically: a zoom shifts groups relative to each other to change focal length, and an internal-focusing design moves only a light interior group rather than the whole barrel. Cementing two elements into one group also removes two air-glass surfaces, reducing flare.
Examples in practice
An internal-focus telephoto moves a single small group, so the barrel neither extends nor rotates — which keeps a polariser in place.