-Canada balsam - liquid resin with a refractive index similar to glass. It is used for bonding elements in compound lenses.
-Candela - unit which expresses the luminous intensity of a light source.
Ektars are also among the earliest lenses to be cemented with thermo-setting synthetic adhesives rather than the traditional Canada Balsam.
Two or more elements which are cemented together (without an air space between them) make a group. (Older lenses used Canada balsam, made from pine pitch, for cement, while newer lenses use higher-tech UV-cured cements.) ...
 See also: Factor, Prism, Simple lens, Plane, Element
  
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