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Photography Question 
Cenk Ceylanoglu
 

untitled


Hi,
What does the elements and groups of the lenses define in digital cameras?
for example :10 elements in 7 groups


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11/22/2001 3:43:46 AM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Cenk,
This is a secification commonly given for film and digital camera lenses (it's not unique to digital cameras). This describes the number of pieces of glass used in the lens and gives a very general idea as to lens complexity and supposedly to how well "corrected" the lens is for aberrations and distortions.

The number of "elements" is the total number of different pieces of glass used. If two or more pieces of glass are cemented together with perfectly mating faces and no air between them, they form a "group." In the example you gave, 10 elements in 7 groups, if you were to completely disassemble the lens you would find 7 pieces of glass with air between them, and upon close examination you would find a few of them to be two pieces of glass cemented together. The reason for doing this is to allow two or more different types of glass (with different indices of refraction) to work together and achieve optically what cannot be done if it were ground from a single piece of the same type of glass.

This many elements and groups leads me to believe it's likely a zoom lens which typically has a higher number of them. More is not necessarily better; glass absorbs light and too much of it reduces contrast. A lens should only have what it takes for adequate aberration correction. Zoom lenses are very complex requiring more glass to provide for both zoom and focusing.

-- John


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11/27/2001 11:44:24 PM

 
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