I have an 360mm Apo-Ronar with a serial number that per Kerry Thalmann's website, makes it date of manufacture around 1958-60. Would this lens be a coated lens? I am not sure what date manufacturers began to coat lenses. Also, would SK Grimes be the best source for purchasing a retaining ring for the lens? It did not come with one. It is in a Compur #2 shutter.