Description
This article is from the
Photographic Lenses FAQ, by David Jacobson with numerous
contributions by others.
29. What are "elements" and "groups", and are more better?
The number of elements is the number of pieces of glass used in the
lens. Single uncemented elements or two or more elements cemented
together are called a group. Thus a lens that has 8 elements in 7
groups has 8 pieces of glass with 2 cemented together. It is
impossible to completely correct all aberrations. Each additional
element the designer has at his/her disposal gives a few more degrees
of freedom to design out an aberration. So one would expect a 6
element lens to be better than a 3 element lens. However, each
surface also reflects a little light, causing flare. So too many
elements is not good either. Note that an unscrupulous manufacturer
could slap together 13 pieces of glass and claim to have a 13 element
lens, but it might be terrible. So by itself the number of elements
is no guarantee of quality.
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photography, lenses, focal length, bellows, focus, pivot
