DIFF Subgroup
G02B 27/021 Full Title
Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 > Viewing or reading apparatus (stereoscopic systems G02B30/00)
G02B 27/021 Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 > Viewing or reading apparatus (stereoscopic systems G02B30/00)