Lens for digital camera

Abstract

A lens assembly, which is mounted on a digital still camera (DSC), comprises a fixed aperture, and a lens unit. The lens unit has a first lens, a second lens, a third lens, a fourth lens and a fifth lens in sequence. The first lens is a negative meniscus lens disposed at the front side of the lens unit. The second lens is a biconvex lens. The third lens is a biconcave lens. The fourth lens is a positive meniscus lens. The fifth lens is a positive lens having a surface, which has a larger curvature radius, facing the image side. The aperture is arranged between the second lens and the third lens.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a camera lens for a camera of fixed focal length and, more specifically, to a lens assembly for use in a digital still camera or PC camera.

BACKGROUND OF THE INVENTION

[0002] Following fast development of personal computer technology, a variety of digital still cameras (DSC) have been disclosed for use with personal computers, and intensively used in families. A regular digital still camera uses a solid state image pickup device such as, charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS), to pick up the image of an object, enabling the image thus obtained to be transferred through a data line to a personal computer, which uses a software program to convert the image into a JPEG, GIF, or TIFF file. In order to meet the tendency of the designing of digital still cameras toward microminiaturization, matching solid-state image pickup devices and related lenses are required to be as small as possible, i.e., the dimensions of the solid-state image pickup devices and the length of the lenses must be minimized. When minimizing the dimensions of a solid-state image pickup device, the overall length of the camera lens must be relatively shortened. According to conventional designs, a camera lens is comprised of a number of lenses axially aligned in a line, and an aperture arranged in between two of the lenses. Because the aperture is spaced between two lenses, the total distance of the camera lens cannot be shorted to the desired level. Furthermore, because a big number of lenses are used, the cost of the camera lens is high.

SUMMARY OF THE INVENTION

[0003] The present invention has been accomplished to provide a lens assembly, which has a simple structure and compact size. The arrangement of the lens unit greatly reduces the optical distortion, improving the image quality.

[0004] According to the primary objective as described above, the lens assembly comprises a fixed aperture, and a lens unit. The lens unit has a first lens, a second lens, a third lens, a fourth lens and a fifth lens in sequence. The first lens is a negative meniscus lens disposed at the front side of the lens unit. The second lens is a biconvex lens. The third lens is a biconcave lens. The fourth lens is a positive meniscus lens. The fifth lens is a positive lens having a surface, which has a larger curvature radius, facing the image side. The aperture is arranged between the second lens and the third lens.

[0005] The lens unit of the lens assembly has the conditions as described hereunder:

0.85<−f1/f<1.8  (1)

1.1<f5/f<1.6  (2)

[0006] Wherein, f1 is the focal length of the first lens, f5 is the focal length of the fifth lens and f is the total focal length of the lens unit.

[0007] The lens unit of the lens assembly has the conditions as described hereunder:

	central
	thickness of	index of
curvature radius (mm)	lens/interval	re-	dispersion	diameter
objective	infinity	Infinity	fraction	confident	(mm)
R1	29.77913	0.45	1.51	64.2	4.76833
R2	3.36455	0.07	1.51	64.2	4.061842
R3	3.673179	1.685764	1.804	46.5	4.061725
R4	−28.00259	0.05	1.804	46.5	3.323749
R5	−5.545101	1.57978	1.80	25.46	3.882636
R6	17.14149	0.5	1.80	25.46	4.548899
R7	−17.00201	0.5437671	1.702	40.2	4.981437
R8	−4.735024	1.80972	1.702	40.2	6.011937
R9	13.98469	0.2	1.800	42.3	7.442676
R10	infinity	1.282319	1.800	42.3	7.553305

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic drawing, showing the arrangement of a lens assembly constructed of a first prefer embodiment of the present invention.

[0009] FIG. 2 is a schematic drawing, showing the lens assembly of the prefer embodiment of the present invention installed in a digital still camera.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0010] Referring to FIG. 1, a lens assembly of the prefer embodiment of the present invention is to be used in a digital still camera or the like, which comprises a fixed aperture 1, and a lens unit 2. The lens unit 2 has a first lens 21, a second lens 22, a third lens 23, a fourth lens 24 and a fifth lens 25 in sequence. The first lens 21 is a negative meniscus lens disposed at the front side of the lens unit 2. The second lens 22 is a biconvex lens. The third lens 23 is a biconcave lens. The fourth lens 24 is a positive meniscus lens. The fifth lens 25 is a positive lens having a surface, which has a larger curvature radius, facing the image side. The aperture 1 is arranged between the second lens 22 and the third lens 23.

[0011] Referring to FIG. 2, the lens assembly of the present invention is installed in the lens holder 3 of a digital still camera (not shown). The lens holder 3 has a cover 31 with a barrel 32 capped in the cover 31, and spacers 4 mounted inside the barrel 32 to hold the lens unit 2 in position.

[0012] The lenses 21 to 25 of the lens unit 1 constructed under the conditions as described hereunder:

0.85<−f1/f<1.8  (1)

1.1<f5/f<1.6  (2)

[0013] Wherein, f1 is the focal length of the first lens 21, f5 is the focal length of the fifth lens 22 and f is the total focal length of the lens unit 2.

[0014] Hereunder I will present the exact data of the lens assembly, wherein the focal length of the lens unit is 10.00 mm and the height of the image is 9.60 mm. The lens assembly of the present invention fits the conditions as shown in the table hereunder:

	central
curvature	thickness of
radius (mm)	lens /interval	index of	dispersion	diameter
object	infinity	infinity	refraction	confident	(mm)
R1	29.77913	0.45	1.51	64.2	4.76833
R2	3.36455	0.07	1.51	64.2	4.061842
R3	3.673179	1.685764	1.804	46.5	4.061725
R4	−28.00259	0.05	1.804	46.5	3.323749
R5	−5.545101	1.57978	1.80	25.46	3.882636
R6	17.14149	0.5	1.80	25.46	4.548899
R7	−17.00201	0.5437671	1.702	40.2	4.981437
R8	−4.735024	1.80972	1.702	40.2	6.011937
R9	13.98469	0.2	1.800	42.3	7.442676
R10	infinity	1.282319	1.800	42.3	7.553305

[0015] In conclusion, the arrangement of the lens assembly greatly reduces the optical distortion, improving the image quality. When used with a CMOS type solid-state image pickup device, the camera cost can be greatly reduced. This design of lens assembly is suitable for use in small digital imaging products such as digital still cameras, and PC cameras.

Claims

1. A lens assembly, comprising an aperture, and a lens unit having a first lens, a second lens, a third lens, a fourth lens and a fifth lens in sequence, said first lens being a negative meniscus lens disposed at said front side of said lens unit, said second lens being a biconvex lens, said third lens being a biconcave lens, said fourth lens being a positive meniscus lens and said fifth lens being a positive lens having a surface, which has a larger curvature radius, facing said image side, said aperture arranged between said second lens and said third lens.

2. The lens assembly as defined in claim 1, wherein said lens unit of said lens assembly has conditions as described hereunder:

3. The lens assembly as defined in claim 1, wherein said lens assembly further has conditions as described hereunder: