1. A zoom lens system having a plurality of lens units, each lens unit being composed of at least one lens element, the zoom lens system, in order from an object side to an image side, comprising:
a first lens unit having negative optical power;
a second lens unit having positive optical power;
a third lens unit having negative optical power; and
a fourth lens unit having positive optical power, wherein
in zooming from a wide-angle limit to a telephoto limit at the time of image taking, the first lens unit moves along an optical axis, and wherein
the second lens unit, in order from an object side to an image side, comprises: a lens element having positive optical power; a lens element having negative optical power; and a lens element having positive optical power, in which air spaces are included between the individual lens elements.
2. The zoom lens system as claimed in claim 1, wherein the following condition (1) is satisfied:
3<fwTL1<70\u2003\u2003(1)
where,
fw is a focal length of the entire system at a wide-angle limit, and
TL1 is an optical axial thickness of a lens element located closest to the object side among the lens elements constituting the first lens unit.
3. The zoom lens system as claimed in claim 1, having:
an escaping lens unit that, at the time of retracting, escapes along an axis different from that at the time of image taking; and
an image blur compensating lens unit that moves in a direction perpendicular to an optical axis in order to optically compensate image blur, wherein
the following condition (2) is satisfied:
3.5<TESCTOIS<18.0\u2003\u2003(2)
where,
TESC is an optical axial thickness of the escaping lens unit, and
TOIS is an optical axial thickness of the image blur compensating lens unit.
4. The zoom lens system as claimed in claim 1, wherein the following condition (3) is satisfied:
\u22121.5<fG1(HT\xd7Z)<\u22120.3\u2003\u2003(3)
where,
fG1 is a focal length of the first lens unit,
HT is an image height at a telephoto limit,
Z is a value expressed by the following formula,
Z=fTfw
fT is a focal length of the entire system at a telephoto limit, and
fw is a focal length of the entire system at a wide-angle limit.
5. The zoom lens system as claimed in claim 1, wherein the following condition (4) is satisfied:
0.3<\u221a(\u2212fG1\xd7fG2)(HT\xd7Z)<2.0\u2003\u2003(4)
where,
fG1 is a focal length of the first lens unit,
fG2 is a focal length of the second lens unit,
HT is an image height at a telephoto limit,
Z is a value expressed by the following formula,
Z=fTfw
fT is a focal length of the entire system at a telephoto limit, and
fw is a focal length of the entire system at a wide-angle limit.
6. The zoom lens system as claimed in claim 1, wherein the first lens unit is composed of two or more lens elements.
7. The zoom lens system as claimed in claim 1, wherein the fourth lens unit is composed of one lens element.
8. The zoom lens system as claimed in claim 1, having
a focusing lens unit that moves relative to an image surface in focusing from an infinity in-focus condition to a close-object in-focus condition, wherein
the focusing lens unit moves to the image side along the optical axis in focusing.
9. The zoom lens system as claimed in claim 8, wherein the focusing lens unit is composed of one lens element.
10. The zoom lens system as claimed in claim 3, wherein the image blur compensating lens unit is composed of one lens element.
11. The zoom lens system as claimed in claim 1, wherein the fourth lens unit is fixed relative to an image surface in zooming from a wide-angle limit to a telephoto limit at the time of image taking.
12. An imaging device capable of outputting an optical image of an object as an electric image signal, comprising:
a zoom lens system that forms an optical image of the object; and
an image sensor that converts the optical image formed by the zoom lens system into the electric image signal, wherein
the zoom lens system is a zoom lens system as claimed in claim 1.
13. A camera for converting an optical image of an object into an electric image signal and then performing at least one of displaying and storing of the converted image signal, comprising
an imaging device including a zoom lens system that forms an optical image of the object and an image sensor that converts the optical image formed by the zoom lens system into the electric image signal, wherein
the zoom lens system is a zoom lens system as claimed in claim 1.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. Agricultural knife apparatus, which is so structured as to be suitable for inserting materials such as seeds into the ground, wherein:
the apparatus is structurally suitable for the operation of creating a slit-opening in the ground and of inserting the materials into the slit-opening, at a depth that is less than about 15 cm vertically below the ground surface;
the apparatus includes a shank and a blade, and includes a transition zone, at which the shank and blade are joined integrally;
the shank includes a front surface and a rear surface, and left and right side surfaces;
when viewed in front elevation, the shank has an axis, termed the shank axis; the blade is formed with an over-surface and an under-surface, which intersect at a line, and the line defines an angled-knife-edge of the blade;
the shank axis intersects the line of the angled-knife edge, at a point of intersection on the angled-knife-edge;
when viewed in front elevation, the line of the angled-knife-edge slopes at an angle, termed the knife angle, relative to the shank axis, and the knife angle is between 30 and 60 degrees;
the angled-knife edge has a bottom extremity thereof, and the distance, measured along the angled-knife-edge, from the point of intersection to the bottom extremity of the angled-knife-edge, is less than about 30 cm.
2. As in claim 1, wherein the angled-knife-edge is a straight line.
3. As in claim 1, wherein the knife apparatus includes a conduit, which is structurally suitable for depositing seeds in the ground, the conduit being attached to, or supported upon, the blade on a back-side of the blade, which is opposite to and remote from the knife-edge.
4. As in claim 1, wherein, in a cross-section of the blade portion taken in a plane at right angles to the knife-edge, the over-surface and the under-surface make an included angle of intersection of between 15 and 30 degrees.
5. As in claim 4, wherein the included angle of intersection is the same at cross-section taken in all planes between the point of intersection and the bottom extremity.
6. As in claim 1, wherein the shank includes an attachment mechanism for attaching the knife apparatus to a mounting bar, the attachment mechanism includes two bolt holes, one above the other, in the shank, and the axis of the shank passes through the bolt holes.