Image pickup lens system

Abstract

An image pickup lens system includes a lens 1 of a meniscus shape having a first face as a convexconcave face, and a diaphragm 2 disposed on an object side of the lens 1. The lens 1 meets the following conditions: Y′ / fl equal to or larger than 0.6; Dt / Dc is equal to or smaller than 0.9 and equal to or larger than 0.5; and Ap2 / Am2 is equal to or larger than 0.9. Thus, even when an image pickup element is of a reduced size, a desired optical performance can be maintained, and it is possible to produce a lens easily with a back focal length ensured.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an image pickup lens system and particularly, to an image pickup lens system of a single lens construction, which is used in an image pickup device (e.g., a CCD camera) utilizing an image pickup element such as CCD, CMOS and the like mounted in a mobile telephone or the like, and which can be reduced in weight and size.[0003]2. Description of the Related Art[0004]In recent years, the multimedia have been developed remarkably, and for example, the demand for a camera utilizing an image pickup element such as CCD, CMOS and the like adapted to be mounted in a portable computer, a visual telephone, a mobile telephone and the like, e.g., a CCD camera, is being increased remarkably. Such a CCD camera is required to be mounted in a limited space and for this reason, it is desired that the CCD camera is small in size and lightweight.[0005]Therefore, it is also desired that an image pickup lens s...

AI Technical Summary

Benefits of technology

[0018]Accordingly, it is an object of the present invention to provide an image pickup lens system, wherein even when the image pickup element is of a reduced size, a desired optical performance can be maintained, and the lens can be produced easily with a back focal length ensured.

[0025]With the first feature of the present invention, a large angle of view can be ensured by setting Y′ / fl in the expression (1) at 0.6 or more. In addition, if Dt / Dc in the expression (2) is larger than 0.9, the refraction force of the lens is insufficient and hence, a desired focal length can not be realized, band in addition, the correction of various aberrations is insufficient. If Dt / Dc is smaller than 0.5, an unbalanced uniformity of the lens thickness is increased and as a result, the formability of the lens is degraded, and it is difficult to work the optical face. Further, the second face of the lens body on the side of the image surface can be utilized effectively by setting Ap2 / Am2 in the expression (3) at 0.9 or more (the maximum value of Ap2 / Am2 is 1.0). In addition, the radius of the optical face can be suppressed to achieve a reduction in size of the lens, and the optical face formed by working can be utilized without any waste, whereby an amount of light in the peripheral portion of the lens can be ensured and hence, an amount of light in the peripheral portion of the lens can be ensured.

[0026]In the present invention, the thickness of the central portion of the lens and the thickness of the peripheral portion of the lens are set in a special relationship by meeting the conditions represented by the expressions (1), (2) and (3). Thus, in a state in which the producible shape of the lens has been maintained, the amount of light in the peripheral portion of the lens can be ensured, and even when the image pickup element is of a reduced size, the performance of the lens can be maintained.

[0029]In the present invention, a telecentric property can be ensured by disposing the diaphragm so as to meet the expression (4) and hence, even when the image pickup element is of a reduced size, a good image picture can be obtained.

[0034]In the present embodiment, the size of the lens can be reduced, and a back focal length can be ensured by meeting the expressions (5) and (6), and when the image pickup element is of a reduced size, the lens can be produced easily.

Problems solved by technology

First of all, in the image pickup element such as CCD, CMOS and the like, 100% of light obliquely entering into the image pickup element cannot be utilized for the structural reason, unlike a silver-salt film and hence, it is required that light enters into a lens at an angle closer to the vertical at any position on the image pickup element. In other words, it is required that a telecentric property is high, and a distance between the image pickup element and a pupil is large.

Therefore, the following problem is encountered: It is extremely difficult that the image pickup lens used in the conventional ¼ inch sensor is reduced in size and used for the / 7 inch sensor.

When the size of the lens is merely reduced, as described above, there is also a problem that the accuracies of the thickness of the central portion of the lens and the thickness of a flange are degraded remarkably.

In this case, however, the following problem is encountered: The size of the entire lens (the thickness and the effective diameter of an optical face) is increased extremely, but also the workability of the lens is degraded.

Further, the back focal length can be improved by forming the lens into a meniscus shape, but there is a problem that if the lens is not of an appropriate shape, the workability of the lens is degraded.

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