Optical Instruments (Balham), misleadingly now in Croydon just outside London, do a lot of work for the Ministry of Defence and are as good as anyone can be. They cleaned my 50/1.2 Canon, transforming its performance , and they have done a lot of work for other people I know too: I have never heard a word against them. I visited the workshop for an article I did for the BJP a few years back and was well impressed. As soon as I get around to it I shall send my 35/2.8 PC-Nikkor and 90/2.5 Vivitar Series 1 Macro to them. They really are very good indeed.