Elements/Groups

I have seen in various lens diagrams the designation elements/groups with numbers like 8/4 (for example). I was wondering whether the element was considered to be two pieces of glass not glued together and a group consists of two or more pieces of glass glued together?

colrehogan said:

I have seen in various lens diagrams the designation elements/groups with numbers like 8/4 (for example). I was wondering whether the element was considered to be two pieces of glass not glued together and a group consists of two or more pieces of glass glued together?

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An element is a single piece of glass. A group consists of two or more pieces of glass glued together.

Your 8 elements in 4 groups example consists of 4 cemented doublets; a cemented doublet is a pair of pieces of glass glued together. The 6/2 G-Claron I put in the mail today consists of two cemented triplets; each half is three pieces of glass glued together. And so on.

Diane,

Every piece of glass is considered an element. A group can be one element, or multiple elements cemented together. So, a 4/4 construction would be a totally air-spaced design with four elements and eight air:glass interfaces (front and back of each element). A 6/4 design has two cemented groups of two elements each, plus two more single elements. Again, it has eight air:glass interfaces. The number of air:glass interfaces is always 2x the number of groups.

Hope that helps.

Kerry

Thanks!