west_matta
Active member
when a lens says it has 4 elements in 3 groups. what does this mean??
groups and elements on a lens?
- Thread starter west_matta
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An element refers to a single lens, which is a piece of glass ground to a particular shape on each side and made from a single piece of glass or other material having a specific refractive index. Refractive index refers to the degree to which the glass can bend light of a particular wavelength.
Two or more elements can be combined (glued or otherwise mounted) to make a group of elements that together provide some optical capability.
Two or more elements can be combined (glued or otherwise mounted) to make a group of elements that together provide some optical capability.
west_matta
Active member
i was still very confused untill i came across this answer....
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.
Thanks J michael
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.
Thanks J michael
ProfessorU
Veteran
Plus you can lose 3% of light per surface of the glass (less with high-quality coatings) so you can get better low-light performance with fewer pieces.