Some Chiyoda Kogaku (aka Chiyoko) cameras of the 1947 to 1949 era featured a blue ⓒ symbol as part of the lens designation like in "ⓒ Super Rokkor", f.e. on the Minolta 35 or the Minolta Memo. It was used to indicate a (single) coated optics rather than any copyright. Similar engravings can be found also on lenses of other manufacturers, f.e. some Olympus Zuiko lenses carry a red-colored "Zuiko C." designation indicating coated optics.
- Kilpatrick, David (2007). "70 years of Minolta - The 1940s and 1950s". Photoclub Alpha. Retrieved 2015-06-07.
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