I was intrigued by this question, mainly due to my passing interest in
photography. So I set out to find something pertaining to this
question. There is an amazing amount of information on the Internet
regarding lenses and SLR cameras and narrowing your searches down to
include only the information about lens elements was still a
challenge.
I tried several searches but the one I had the most luck with is this
one
science "lens elements" comparison camera
://www.google.ca/search?hl=en&ie=UTF-8&oe=UTF-8&q=science++%22lens+elements%22+comparison+camera&meta=
3rd down the list in this search gave me this link
http://people.smu.edu/rmonagha/mf/elements.html
which talks about the advantages of each configuration and the reasons
why more elements are even used.
Here is an excerpt from that very same page
Origins of the Mystique Behind Lens Elements and Groups
In the past, the number of elements and groups in a lens was
frequently part of the published specifications of the lens.
Photographers used such information as a key to the cost and
complexity of the lens. The use of more than four elements provided
the optical designer with more freedom to control lens aberrations and
improve the speed of the lens too.
The number of groups helped indicate whether the lens elements were
separate or glued together into multi-element lens components. If a
lens had 5 elements and 5 groups, that meant it had each of the five
glass elements separately mounted with air spaces between them.
But with a design in which the lens has 5 elements in 3 groups, we
can't tell how the elements are setup internally. For example, 5
elements can be made into 3 groups by having the first three elements
cemented togther, the middle three cemented together, or the last
three cemented together, or combinations of two pairs of lenses
cemented together with a single element, and so on.
That's why internal lens diagrams are needed to evaluate the internal
lens configuration and identify its design type and probable strengths
and weaknesses. But today, photographers no longer concern themselves
with the design of their lenses, just with how well they work and how
much they cost!
Simple lenses usually have their elements mounted together in a rigid
lens cell to maintain the needed high precision positioning of lens
elements demanded by the lens design. The entire lens is moved during
focusing. A few lens designs (e.g., in some folder cameras) moved some
of the front lens elements, but not all of them, during focusing. Such
designs often proved troublesome in practice. Today's modern prime
zoom lens designs require various floating element (e.g., Nikon's CRC
close focusing correction) and moving elements in internal focusing
(e.g., Nikon's ED-IF..) designs using complex mechanics to achieve
precision movements.
As photographers, we know that each air-glass interface offers a
potential for flare. The more such air-glass interfaces in the lens,
the more flare and the lower the lens contrast was likely to be. So
combining lenses into groups cemented together removed or reduced the
number of air-glass interfaces. The natural presumption was that these
cemented lens designs improved the flare and contrast over similar
air-spaced lens designs.
If you look at improvements in lens designs over time in prime lenses
(e.g., Nikon), you find the earlier designs of the 60's and 70's
giving way to more and more complex multi-element lenses. Extra
elements were added to improve on close focusing or reduce aberrations
or vignetting in an already useful design.
The practice of counting lens elements and groups has fallen out of
favor, largely because of new low dispersion glasses. Thanks to such
improved glasses, it is now possible to reduce the number of elements
in many lens designs, while improving the lens in many aspects.
Internal focusing designs have also changed the priorities of lens
designers. A lens with fewer elements may now be better corrected,
thanks to the new optical glasses. Computer lens design programs could
also generate lenses with better performance and fewer elements by
trying milliions of possible design combinations, something past lens
designers couldn't easily try.
The biggest change has probably come about with the development of
zoom lenses. While zoom lenses offer convenience, they still have more
elements (often 12, 14 or more) and groups and hence more flare and
lower contrast than most prime lenses. Because of the complexity of
zoom lens designs, we have given up trying to guesstimate their
quality from their number of lens elements or groups.
However, several facts remain to be discerned from the number of lens
elements and groups. A simpler lens with fewer elements (such as a
prime) will generally have lower levels of flare and higher contrast
than a more complex lens (e.g., zoom) with many more elements and
groups - other factors such as cost and quality of construction and
multicoating being equal. This fact is one major reason that medium
format and large format users so often use prime lenses to achieve the
highest levels of optical quality. Even today (AD 2000), we are only
seeing a handful of very expensive pro zoom lenses which are close
enough to the quality of prime lenses as to be used in some or many
professional applications.
Make sure you visit this page because it has much more information
about lenses etc… that is absolutely fascinating. |
