Nikkor Lens Letters ?

[klop]

At the risk of sounding ignorant, some nikkor lenses I have seen (older lenses) have a letter or letters after Nikkor on the lens ring...... What is the significance?

 

[darkosaric]

https://en.wikipedia.org/wiki/Nikon_F-mount

... Tres (3), Quattuor (4), Penta (5), Hex (6), Septem (7), Octo (8), Novem (9), UnDecim (11), QuattuorDecim (14) and Penta-Decem (15) ...

designating the number of optical elements in the design

 

[klop]

Thank You, link answers everything.......