Two-group zoom lens
View Patent ↗A two-group zoom lens includes, in order from the object side, a first lens group that includes a negative lens component formed of a negative plastic lens element having at least one aspheric lens surface and a positive lens component, and a second lens group that includes a diaphragm, a positive lens component that is formed of a positive plastic lens element having at least one aspheric lens surface, and a negative lens doublet component. The first lens group and at least a part of the second lens group is movable along the optical axis for zooming, and either the first lens group or a lens component of the second lens group moves independently of the other lens components of the second lens group for focusing. Except for the negative lens doublet component, each lens component may be a lens element. The lens components and lens elements satisfy certain conditions.
1. A zoom lens formed of only two lens groups, in order from the object side, as follows:
a first lens group; and
a second lens group;
wherein
the first lens group includes, in order from the object side, a first lens component of negative refractive power that includes a negative plastic lens element having at least one aspheric lens surface, and a second lens component of positive refractive power;
the second lens group includes, in order from the object side and without any intervening lens elements, a diaphragm for controlling the light that passes through the zoom lens, a third lens component of positive refractive power that includes a convex lens surface on its object side and that includes a positive plastic lens element having at least one aspheric lens surface, a fourth lens component that includes only two lens elements that are, in order from the object side, a fourth lens element of negative refractive power and a fifth lens element that, together, form a lens component doublet, and a fifth lens component that is a negative lens component; and
the first lens group and at least part of the second lens group are movable along the optical axis for zooming, and said fifth lens component is movable along the optical axis for focusing independent of movement of the other lens components of said second lens group.
2. The zoom lens of claim 1 , wherein said first lens component consists of said negative plastic lens element and both lens surfaces of the said negative plastic lens element are aspheric lens surfaces, and said third lens component consists of said positive plastic lens element and both lens surfaces of said positive plastic lens element are aspheric.
3. The zoom lens of claim 1 , wherein the following conditions are satisfied:
−25 <f 6 /fw<− 15
−0.04 <fw/R 1<0
where
f 6 is the focal length of said fifth lens component;
fw is the focal length of the zoom lens at the wide-angle end; and
R 1 is the radius of curvature of the object-side lens surface of said first lens component.
4. The zoom lens of claim 2 , wherein the following conditions are satisfied:
−25 <f 6 /fw<− 15
−0.04< fw/R 1<0
where
f 6 is the focal length of said fifth lens component;
fw is the focal length of the zoom lens at the wide-angle end; and
R 1 is the radius of curvature of the object-side lens surface of said first lens component.
5. The zoom lens of claim 3 , wherein the following condition is satisfied:
1.7 <f 3/ fw< 2.2
where
f 3 is the focal length of said third lens component.
6. The zoom lens of claim 4 , wherein the following condition is satisfied:
1.7 <f 3/ fw< 2.2
where
f 3 is the focal length of said third lens component.
7. The zoom lens of claim 1 , wherein:
the absolute value of the radius of curvature of the lens surface on the object side of said fourth lens element is smaller than the absolute value of the radius of curvature of the lens surface on the image side of said fourth lens element; and
said fifth lens element is a biconvex lens element.
8. The zoom lens of claim 7 , wherein said first lens component and said third lens component together include at least three aspheric lens surfaces.
9. The zoom lens of claim 1 , wherein the zoom lens includes only five lens components.
10. The zoom lens of claim 9 , wherein the zoom lens includes only six lens elements.