Compact zoom lens
View Patent ↗A compact zoom lens includes, in order from an object side to an image side, a first lens group ( 1 ) of negative refractive power, and second, third, fourth and fifth lens groups ( 2, 3, 4, 5 ) of positive refractive power. The second, third and fourth lens groups are movable to effect zooming and focusing. During zooming from the telephoto end to the wide-angle end, the fourth lens group moves from the object side to the image side. The compact zoom lens has a long back focal length with various aberrations satisfactorily corrected, and a small F-number for enhanced image brightness.
1. A zoom lens comprising, in order from an object side to an image side, a first lens group of negative refractive power, a second lens group of positive refractive power, a third lens group of positive refractive power, a fourth lens group of positive refractive power and a fifth lens group of positive refractive power; wherein, during zooming from the telephoto end to the wide-angle end, the fourth lens group moves from the object side to the image side, and the zoom lens satisfies the following condition:
0.499
<
fa
bf
where fa represents the focal length of the zoom lens at the wide-angle end, and bf represents the back focal length of the zoom lens at the wide-angle end.
2. The zoom lens as claimed in claim 1 , wherein, during zooming from the wide-angle end to the telephoto end, the second lens group moves from the object side to the image side.
3. The zoom lens as claimed in claim 2 , wherein, during zooming from the wide-angle end to the telephoto end, the third lens group moves from the object side to the image side.
4. The zoom lens as claimed in claim 3 , wherein the fourth lens group moves toward the image side at the same velocity as the third lens group.
5. The zoom lens as claimed in claim 1 , satisfying the following condition:
tt
fa
<
6.36
where tt represents the total track of the zoom lens at the wide-angle end, and fa represents the focal length of the zoom lens at the wide-angle end.
6. The zoom lens as claimed in claim 5 , satisfying the following condition:
tt
bf
<
3.17
where tt represents the total track of the zoom lens at the wide-angle end, and bf represents the back focal length of the zoom lens at the wide-angle end.
7. The zoom lens as claimed in claim 6 , satisfying the following condition:
ex
bf
<
8.153
where ex represents the exit pupil position of the zoom lens at the wide-angle end, and bf represents the back focal length of the zoom lens at the wide-angle end.
8. The zoom lens as claimed in claim 7 , satisfying the following condition:
0.685
<
lt
tt
where lt represents the overall length from a front vertex of the first lens element to a rear vertex of the last lens element of the zoom lens at the wide-angle end, and tt represents the total track of the zoom lens at the wide-angle end.
9. The zoom lens as claimed in claim 1 , wherein the first to fifth lens groups include at least one aspheric lens element.
10. The zoom lens as claimed in claim 9 , wherein the fourth lens group includes an aspheric lens element.
11. The zoom lens as claimed in claim 10 , wherein the first lens group includes an aspheric lens element.
12. The zoom lens as claimed in claim 11 , wherein said aspheric lens element is made of plastic.
13. The zoom lens as claimed in claim 12 , wherein the spherical lens elements of the first to fifth lens groups are made of glass.
14. The zoom lens as claimed in claim 13 , further comprising an aperture stop disposed in the fourth lens group.
15. The zoom lens as claimed in claim 14 , wherein the first lens group comprises a first lens element having a convex object-side surface and a concave image-side surface.
16. The zoom lens as claimed in claim 15 , wherein the first lens group further comprises a second lens element having a convex object-side surface and a concave image-side surface.
17. The zoom lens as claimed in claim 16 , wherein the first lens group further comprises a third biconcave lens element.
18. The zoom lens as claimed in claim 17 , wherein the second lens group consists of a fourth lens element, the fourth lens element having a convex object-side surface and a convex image-side surface.
19. The zoom lens as claimed in claim 18 , wherein the third lens group consists of a fifth lens element, the fifth lens element having a convex object-side surface and a slightly convex image-side surface.
20. The zoom lens as claimed in claim 19 , wherein the fourth lens group comprises a biconcave sixth lens element.
21. The zoom lens as claimed in claim 20 , wherein the fourth lens group further comprises a biconvex seventh lens element.
22. The zoom lens as claimed in claim 21 , wherein the fourth lens group further comprises an eighth lens element, the eighth lens element having a slightly concave object-side surface and a convex image-side surface.
23. The zoom lens as claimed in claim 22 , wherein the fifth lens group consists of a nineth lens element, the nineth lens element having a convex object-side surface and a substantially planar image-side surface.