| 摘要 |
PURPOSE:To prevent a focus from moving in accordance with fluctuations of temperature over the entire variable magnification range by constituting at least one of groups, constituting a magnification variation system, by inorganic glass, and then canceling temperature aberration generated by a plastic lens. CONSTITUTION:A system consists of the 1st positive group G1 for focusing, the 2nd negative group G2 as a variator, the 3rd positive group G3 as a compensator, and the 4th positive group G4, and has a 3 zoom ratio and a 3F value. The G1 consists of a negative lens L1 of polystyrene and a positive lens L2 of acryl, and the G2 consists of a negative lens L4 of acryl, a negative lens L5 of acryl, and a positive lens L6 of inorganic glass; and the G3 consists of a positive lens L7 of acryl, and the G4 consists of a positive lens L8 of inorganic glass, a negative lens L9 of polystyrene, and positive lenses L10 and L11 of acryl. An independent lens in the magnitude variation system which has a temperature aberration coefficient equal to the extent of variation of the whole system is substituted for glass. |
