Originally Posted by
Dan Fromm
A plasmat has six elements in four groups. The outer two groups are cemented doublets, the inner group is a singlet. A dagor type has six elements in two groups. Each group is a cemented triplet.
To tell whether a lens is a plasmat type or a dagor type, take a single cell, shine a point source of light into it and count reflections. A plasmat cell will have four strong reflections, one from each of the four air-glass interfaces, and one weak reflection, from the glass-cement-glass interface. Weak reflections are often hard to see. A dagor cell will have two strong reflections and two weak ones. Again, the weak reflections can be hard to see.
In the G-Claron line, dagor types (serial number probably < 12,000,000) were replaced by plasmat types (s/n probably >= 12,000,000) in the early 1970s. There's considerable doubt about where the s/n break is. Count reflections unless the s/n is > 13,000,000.
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