Patent ID: 7626764

Claim:
A projecting lens system comprising, in this order from the screen-side thereof: a first lens positive in power, a second lens negative in power, a third lens positive in power, and a fourth lens positive in power; the projecting lens system meeting a criteria of 1.4<TT/f<1.7; where TT denotes a total length of the projecting lens system and f denotes an effective focal length of the projecting lens system, wherein the specifications of the projecting lens are listed in the following table: Radius of Protecting lens curvature Thickness Reflective Abbe system100 (mm) (mm) index number Screen-side 28.05737 12 1.696797 55.5322 surface of the first lens 10 SLM-side 35.18796 22.53765 — — surface of the first lens 10 Aperture ∞ 7.933927 — — stop 60 Screen-side −14.61593 9.688149 1.84666 23.7779 surface of the second lens 20 SLM-side −22.67261 1 — — surface of the second lens 20 Screen-side ∞ 12 1.696797 55.5322 surface of the third lens 30 SLM-side −47.49873 53.24028 — — surface of the third lens 30 Screen-side 67.60116 12 1.5168 64.1673 surface of the fourth lens 40 SLM-side ∞ 3 — — surface of the fourth lens 40 wherein TT=135 mm, f=82.91 mm, BFL3=66.83 mm, f4=124.74 mm, AVE (Vb 1 - 3 )=55.5322, FNo=3.41, and 2ω=33.72°, where TT denotes a total length of the projecting lens system, f represents a focal length of the projecting lens system, BFL 3 denotes a back focal length of the projecting lens system, AVE (Vb 1 - 3 ) denotes an average value of Abbe numbers of the first lens and the third lens, FNo represents the aperture F-number, and 2ω represents a field angle of the projecting lens system.