Abstract A projection lens in which F is approximately 1.0 to 1.3 used for a 3-tube television projector. The projection lens comprises a first lens of extremely low refractive power, two positive lenses arranged spaced apart from the first lens through a large air space and a negative fourth lens arranged spaced apart therefrom through a large air space, the first lens L 1 having at least one surface in the form of an aspherical surface. It is possible to arrange a reflecting mirror in the large air space to thereby form an optical system into a compact form. In addition, if the second lens L 2 and the third lens L 3 are made of glass, even if the first lens L 1 and the fourth lens L 4 are formed into plastic lenses, movement of focal point due to variation in temperature hardly occurs, and a lens of low cost may be obtained.
A lens for projecting a television image na screen comprising, in order from said screen, a first lens L 1 of small refractive power, a second lens L 2 of positive power spaced apart from the first lens through a large air space, a third lens L 3 of positive power and a fourth lens L 4 of negative power spaced apart from the third lens through a large air space, a side of a, at least one surface of the first lens L 1 being in the form of as aspherical surface, said lens for projecting fulfilling the following conditions: -0.1<f/f.sub.1 <0.1 0.5<f.sub.3 /f.sub.2 <1.5 -0.8<f/n.sub.4 f.sub.4 <-0.4 where f: focal length of the whole system fi: focal length of the i lens L i n4: refractive index of the 4th lens L 4
Claim 2
Dependent Claim
135 words
A lens for projecting a television image na screen comprising, in order from said screen, a first lens L 1 of small refractive power, a second lens L 2 of positive power spaced apart from the first lens through a large air space, a third lens L 3 of positive power and a fourth lens L 4 of negative power spaced apart from the third lens through a large air space, a side of a, at least one surface of the first lens L 1 being in the form of as aspherical surface, said lens for projecting fulfilling the following conditions: -0.1<f/f.sub.1 <0.1 0.5<f.sub.3 /f.sub.2 <1.5 -0.8<f/n.sub.4 f.sub.4 <-0.4 where f: focal length of the whole system fi: focal length of the i lens L i n4: refractive index of the 4th lens L 4
Claim 3
Dependent Claim
38 words
The lens according to claim 1, wherein the second lens L 2 and the third lens L 3 comprise a glass lens, and the first lens L 1 and the fourth lens L 4 comprise a plastic lens.
Claim 4
Dependent Claim
36 words
The projection lens according to claim 1, wherein the space d 6 between the third lens L 3 and the fourth lens L 4 fulfilled fulfills the following: f<F·d.sub.6 where F is F number of lens.