By "long radius", I am talking about the HR optic SP spec'd for the 921. The document I have describing the 921 is the 1978 Spectra Physics publication describing all of their ion lasers. While it gives part numbers for all the 164, 165, 166 and 171s, it does not give me a part number for the 921. It just says "Long Radius High Reflector". What can you tell me about the HR and OC optics for the 921?