I read long ago that both Nikon and Canon double coated and multi coated lenses before Pentax stared advertising multi coated lenses. I've seen a 45 GN that was multi coated but lacked a C to indicate multi coating. It's possible that a surfaces are not multi coated. Given the way Nikon produced there run of a lens then didn't return to that lens for many months they probably wanted to sell down their single coated inventory before advertising multi coated lenses.
I wonder how much is known about when specific lenses had unadvertised upgrades to their coatings?
It is possible the serial number ring (with the "C" designation) has been swapped between single and multi-coated lenses during repair. The single coated 45GN has amber and purple coatings, while the multi-coated version has darker green-blue-purple coatings.
I know of three Nikkors which are multi-coated and lack the "C" to indicate multi coating:
- Nikkor-S 55/1.2 multicoated on one (?) of the rear elements, shows as a green reflection at certain angles - unlike the amber, blue and pink of single coated lenses. Some claim this was the first to be multi-coated. I have no information about when this was introduced, it was probably a silent upgrade. It is at least found on later lenses marked "Nippon Kogaku Japan" dating from the very late 1960s or 1970.
- Nikkor-N 35/1.4 - first Nikkor to be multi-coated on all lens surfaces, from 1970. The first series are marked the old style "Nikkor-N Nippon Kogaku Japan", then "Nikkor-N Nikon", and finally "Nikkor-N.C Nikon" which acknowledges the multi-coating.
- Nikkor-N 28/2 - Second Nikkor to be multi-coated on all lens surfaces, released a few months after the 35/1.4, but with similar history.
All other fully multi-coated lenses were already introduced with the "C" designation.
It seems at first Nikon considered multi-coating like Nano Crystal Coating of today, to be applied only to specific surfaces to control flare and that otherwise single-coated lenses were sufficient. Perhaps they later realised that multi-coating was cheap enough and robust enough to be applied to all surfaces. And even later the marketing department realised it might be good to advertise the new coating by putting a "C" on the lens!
I also wonder if some of the older lenses were more than just single-coated. Some of the later so-called single-coated lenses have coatings with darker reflections and more colours than earlier lenses. For example the gauss Nikkor-P 105/2.5 and newer Nikkor-Q 135/3.5 (7 aperture blades) have coatings which are a deeper blue than the older Nikkor-Q 135/3.5 (6 aperture blades), which suggests an improvement in coating.
Also the Nikkor-UD 20/3.5 has purple-amber coatings which seem surprisingly transparent for a single coated lens, and strangely there is no multi-coated Nikkor-UD.C version. Was it was already multicoated (or at least double coated)? The following 20/4 belongs to an era when all lenses were multi-coated, yet the coatings look very similar to the older 20 UD ...
