Projection lens
A projection lens disposed between an enlarged side and a reduced side and including a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having positive refractive power, and an optical element disposed between the second and the third lens groups is provided. The first lens group includes a first and a second lens sequentially arranged from the enlarged side to the reduced side and respectively having a positive and a negative refractive power. The second lens group between the first lens group and the reduced side includes a third, a fourth, a fifth, and a sixth lens sequentially arranged from the enlarged side to the reduced side. The fifth and the sixth lens respectively have a positive refractive power. The third lens group disposed between the second lens group and the reduced side includes a seventh lens.
1. A projection lens, disposed between an enlarged side and a reduced side, the projection lens comprising:
a first lens group, having a negative refractive power, and comprising a first lens and a second lens sequentially arranged from the enlarged side to the reduced side, wherein the first lens and the second lens respectively have a positive refractive power and a negative refractive power;
a second lens group, having a positive refractive power, disposed between the first lens group and the reduced side, and comprising a third lens, a fourth lens, a fifth lens, and a sixth lens sequentially arranged from the enlarged side to the reduced side, wherein the fifth lens and the sixth lens respectively have a positive refractive power;
a third lens group, having a positive refractive power, disposed between the second lens group and the reduced side, and comprising a seventh lens; and
an optical element, disposed between the second lens group and the third lens group.
2. The projection lens according to claim 1 , wherein an effective focal length of the first lens group is f G1 , an effective focal length of the projection lens is f, and the projection lens satisfies 4.5<|f G1 /f|<8.
3. The projection lens according to claim 1 , wherein an effective focal length of the first lens group is f G1 , an effective focal length of the first lens is f G1S1 , and the projection lens satisfies 0.15<|f G1S1 /f G1 |<0.6.
4. The projection lens according to claim 1 , wherein the third lens and the fourth lens respectively have a negative refractive power and a positive refractive power, an Abbe number of the third lens is ν3, an Abbe number of the fourth lens is ν4, and 20<|ν3−ν4|<36.
5. The projection lens according to claim 1 , wherein the first lens group and the second lens group are suitable for moving relative to the third lens group to focus.
6. The projection lens according to claim 1 , wherein the third lens group is fixed relative to the projection lens.
7. The projection lens according to claim 1 , wherein the sixth lens is an aspheric lens.
8. The projection lens according to claim 1 , wherein the seventh lens is an aspheric lens.
9. The projection lens according to claim 1 , wherein the first lens and the second lens are spherical lenses.
10. The projection lens according to claim 1 , wherein the third lens and the fourth lens are spherical lenses.
11. The projection lens according to claim 1 , wherein the fifth lens is a spherical lens.
12. The projection lens according to claim 1 , wherein the first lens is a concavo-convex lens having a convex side facing the enlarged side, and the second lens is a biconcave lens.
13. The projection lens according to claim 1 , wherein the third lens is a biconcave lens, and the fourth lens is a biconvex lens.
14. The projection lens according to claim 1 , wherein the third lens and the fourth lens form a double cemented lens.
15. The projection lens according to claim 1 , wherein the fifth lens is a biconvex lens.
16. The projection lens according to claim 1 , wherein the optical element is a prism.
17. The projection lens according to claim 1 further comprising:
an aperture diaphragm, disposed between the first lens group and the second lens group.
18. The projection lens according to claim 17 , wherein a distance from the first lens group to the aperture diaphragm is L 1 , an effective focal length of the projection lens is f, and the projection lens satisfies 0.24<L 1 /f<0.3.
19. The projection lens according to claim 7 , wherein the first lens group, the aperture diaphragm, and the second lens group are suitable for moving relative to the third lens group to focus.