| 摘要 |
PROBLEM TO BE SOLVED: To put the lens device in focus corresponding to screen size over a wide range and to maintain high performance over the entire diagonal length range of the screen by specifying the lens constitution. SOLUTION: The device consists of a 1st lens unit with refracting powerΦ1 which compensates aberrations depending upon an aperture, a 2nd lens unit with refraction powerΦ2 , a compensating lens unit with refracting powerΦCR, and a 3rd lens unit which compensates curvature of field and is in contact with coupling liquid in order form the image side. The refracting power of the 3rd lens unit and coupling liquid isΦ3 , and the refracting power of the coupling liquid isΦ; andΦ1 >0,Φ2 /Φ>0.7,ΦCR<0, andΦ3 <0 hold. The 1st lens unit has surfaces S1 to S4 and the 2nd lens unit has surfaces S5 to S12; and the compensating lens unit has surfaces S13 and S14 and the 3rd lens unit has surfaces S15 to S18. The face plate of a CRT forms surfaces S17 and S18.
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