(19)

(11)

EP 0 406 339 A1

(12)

(43) Date of publication: 09.01.1991 Bulletin 1991/02 (21) Application number: 89909817.0 (22) Date of filing: 23.08.1989

(51) International Patent Classification (IPC):  G02B 6/ 30( . ) G02B 6/ 42( . ) G02B 6/ 38( . ) (86) International application number: PCT/GB1989/000979 (87) International publication number: WO 1990/002351 (08.03.1990 Gazette 1990/06)

(84) Designated Contracting States: AT BE CH DE FR GB IT LI LU NL SE (30) Priority: 23.08.1988 GB 19880019983 (71) Applicant: BT&D TECHNOLOGIES LIMITED Ipswich, Suffolk IP1 5PB (GB)	(72) Inventors: HARMON, Robert, Arthur Woodbridge Suffolk IP13 6UT (GB) PRESTON, Keith, Robert Woodbridge Suffolk IP12 1LF (GB) ROSE, Peter, John Ipswich Suffolk IP5 7ET (GB) (74) Representative: Wolff, Eric  BT&D Technologies Ltd Whitehouse Road Ipswich, Suffolk IP1 5PB Ipswich, Suffolk IP1 5PB (GB)