Elements & Groups
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A lens element is a single piece of glass or optical plastic, the term is short for 'optical element'. A group is a collection of one or more elements.
So a camera lens that has 16 elements in 12 groups has 16 optical elements arranged in to 12 distinct optical groupings.
An illustration might help you understand this concept better.
Originally posted by Ian
hmm..so is this 11 elements in 6 groups?
why the manufacturers usually put up the number or elements and groups in the spec of the lens? as an user, why will you interested to know abt this?
how will number of elements and groups affect the performance?
I guess different groups of elements have different functions? some for focusing..some for zooming??
I guess less elements better?? lesser distortion and less light being reflected or cut off
I am just interested to know...so dun flame me if i am wrong ok.
Nope, it's 16 elements in 11 groups as the diagram doesn't show the individual elements making up some of the compound elements.
It's as much to do with marketing as anything else, people seem to be impressed by the number of chunks of glass and plastic in their lenses. It also helps explain to customers where their money is going. To be fair though for very experienced photographers etc it also can give a good idea of the optical complexity of the camera lens.
This is a very complex issue and there's no easy answer! While there's no direct correlation between the number of elements and groups in a lens and it's optical performance this statement has to be qualfied by stating that the number of elements and groups is largely determined by the amount of optical correction required, lens speed (aperture) and overall optical design of the lens.
For example, the Zeiss Tessar design of 4 elements in 3 groups is one of the most widely copied designs for medium and large format camera and gives excellent results over quite a large range of focal lengths.
Some of Nikons best lenses are also quite simple designs, such as the 55/3.5 Micro (macro) lens, which is a 5 element desing in 4 groups, or the 105/2.5 which is also a 5/4 design.
Whereas the 13/5.6 Nikkor required 16 elements in 12 groups and the AF-D 20/2.8 uses 12 elements in 9 groups.
More or less on track here. Generally speaking top end zoom lenses have a far more complex optical design than their fixed focal length cousins.
Not always, in optics overall performance is determined by the design requiremens and its implementation. This is largely restricted by the types of materials available for the lens elements and cost of manufacture.
The use of multicoating on lens elements reduces significantly the amount of internal reflections and boosts light transmission signficiantly thus allowing optical designers to create complex optical designs without incurring massive light losses.
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