Optical system

Disclosed is an optical system. The optical system includes first to fifth lenses sequentially arranged from an object side to an image side. The optical system satisfies 1.5<n2<1.55, 50<v2<70, and 20<v3<30 in which n2 represents a refractive index of the second lens, v2 represents an abbe number of the second lens, and v3 represents an abbe number of the third lens.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2011-0088194, filed Aug. 31, 2011, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The embodiment relates to an optical system.

BACKGROUND ART

Recently, a portable phone or a mobile communication terminal is equipped with a compact digital camera or a digital video camera employing a solid state image sensor, such as a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor) image sensor. Such an image sensor has become scaled-down, so that an optical system used for the image sensor is needed to have a small size and high performance.

In addition, an optical system according to the related art includes first to fourth lenses, a filter, and a light receiving device. In this case, the first to fourth lenses are sequentially arranged upward from an object side. In addition, the first and third lenses may have positive refractive power, and the second and fourth lenses may have negative refractive power. In addition, the second lens may be designed so that the refractive power of the second lens is greater than that of other lenses.

The first lens may have a surface convex toward the object side, and the second lens may have a surface concave toward an image side. The filter may include an infrared filter, and the light receiving device may include a CCD image sensor or a CMOS image sensor.

The above small optical system is disclosed in Korean Patent Application No. 10-2007-0041825.

Technical Problem

The embodiment provides an optical system representing improved performance and a small size.

Technical Solution

According to the embodiment, there is provided an optical system including first to fifth lenses sequentially arranged from an object side to an image side, wherein the optical system satisfies following Equation 1,
1.5<n2<1.55
50<v2<70
20<v3<30  Equation 1

in which n2represents a refractive index of the second lens, v2represents an abbe number of the second lens, and v3represents an abbe number of the third lens.

According to the embodiment, the optical system satisfies following Equation 3,
0.8<f1/F<1.2  Equation 3

in which f1represents an effective focal distance of the first lens.

According to the embodiment, the optical system satisfies following Equation 4,
φ4>φ1>φ2  Equation 4

in which φ1, φ2, and φ4represent refractive power of the first lens, refractive power of the second lens, and refractive power of the fourth lens, respectively.

According to the embodiment, the optical system may further include an aperture interposed between the first and second lenses.

According to the embodiment, the first, second, and fourth lenses may have positive refractive power, and the third and fifth lenses may have negative refractive power.

According to the embodiment, sides of the first to fifth lenses facing the object side and sides of the first to fifth lenses facing the image side may be aspheric surfaces.

Advantageous Effects

As described above, when the optical system of the embodiment is designed as described above, the optical system can satisfy following Equation 2.
1<tt1/F<1.3  Equation 2

In Equation 2, tt1represents a distance from the surface facing the object of the first lens10to the surface facing the image of the fifth lens on the optical axis of the lens system and F represents the whole effective focus length. As described above, the distance from the surface of the first lens facing the object of the first lens to the surface of the fifth lens facing the image of the fifth lens may represent a very small value.

Accordingly, the optical system according to the embodiment can represent improved performance and a small size.

BEST MODE FOR INVENTION

Hereinafter, an image sensor according to the embodiment will be described in detail with reference to accompanying drawings.

FIG. 1is a side sectional view schematically showing the internal structure of a small optical system according to the embodiment.

Referring toFIG. 1, the small optical system according to the embodiment includes a first lens10, an aperture15, a second lens20, a third lens30, a fourth lens40, a fifth lens50, a filter60, and a light receiving device70which are sequentially arranged from an object side to an image side.

In order to obtain the image of an object, light corresponding to image information is incident onto the light receiving device70after passing through the first lens10, the aperture15, the second lens20, the third lens30, the fourth lens40, the fifth lens50, and the filter60.

The first and send lenses10and20may have a positive refractive power. The third lens30may have a negative refractive power, and the fourth lens40may have a positive refractive power. The fifth lens50may have a negative refractive power.

In this case, the first lens10, the second lens20, and the fourth lens40may satisfy following Equation 4.
φ4>100 1>φ2  Equation 4

In Equation 4, φ1, φ2, and φ4represent refractive power of the first lens10, the refractive power of the second lens20, and the refractive power of the fourth lens40, respectively.

In addition, the first to fifth lenses10to50may include glass or plastic.

A side R1of the first lens10facing an object side may have a convex shape, and a side R2of the first lens10facing an image side may have a concave shape. The side R1of the first lens10facing the object side and the side R2of the first lens10facing the image side may have an aspheric surface. In addition, the first lens10may have the shape of a meniscus.

The focus length of the first lens10may satisfy following Equation 3.
0.8<f1/F<1.2  Equation 3

In Equation 3, f1represents an effective focal distance of the first lens10, and F represents a whole focal distance of a small optical system according to the embodiment.

In more detail, the focal distance of the first lens10may satisfy following Equation 5.
0.9<f1/F<1.1  Equation 5

The second lens20may have the shape of a meniscus. A side R4of the second lens20facing the object side may have a concave shape, and the side R5of the second lens20facing the image side may have a convex shape. In addition, the side R4of the second lens20facing the object side and the side R5of the second lens20facing the image side may have an aspheric surface.

The refractive index n2of the second lens20may be in the range of about 1.5 to about 1.55. In detail, based on a line d, the refractive index n2of the second lens20may be in the range of about 1.5 to about 1.55. In more detail the refractive index n2of the second lens20may be in the range of about 1.54 to about 1.55.

In addition, an abbe number v2of the second lens20may be greater than about 50. In detail, the abbe number v2of the second lens20may be in the range of about 50 to about 70. In more detail, the abbe number v2of the second lens20may be in the range of about 55 to about 65.

Both sides of the third lens30may have a concave shape. A side R6of the third lens30facing the object side may have a concave shape, and a side R7of the third lens30facing the image side may have a concave shape. In addition, the side R6of the third lens30facing the object side and the side R7of the third lens30facing the image side may have an aspheric surface.

An abbe number v3of the third lens20may be in the range of about 20 to about 30. In more detail, the abbe number v3of the third lens30may be in the range of about 23 to about 27.

The fourth lens40may have the shape of a meniscus. A side R8of the fourth lens40facing an object side may have a concave shape, and a side R9of the fourth lens40facing an image side may have a convex shape. The side R8of the fourth lens40facing the object side and the side R9of the fourth lens40facing the image side may have an aspheric surface.

The fifth lens50has at least one aspheric inflection point.

In this case, at least one aspheric inflection point may be formed at a side R10of the fifth lens50facing the objection side. In addition, at least one aspheric inflection point may be formed at a side R11of the fifth lens50facing the image side. The aspheric inflection point formed in the fifth lens50can adjust the maximum of an incident angle of main ray incident to the light receiving device70.

If the light receiving device70serving as an imaging surface R14is a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), an angle to ensure the quantity of light exists with respect to each pixel. If a different angle is used in the pixel, the quantity of light is not ensured, a shading phenomenon in which an outer portion of the image is darkened.

Therefore, according to the present embodiment, the maximum of incident angle of the main ray is adjusted by forming the aspheric inflection point at a side R11of the fifth lens50facing the image side, thereby preventing the outer portion of the image screen from being darkened.

The aperture15is interposed between the first lens10and the second lens20to converge selectively incident light so that a focus length can be adjusted.

The filter60may include an infrared cut filter (IR cut filter)60. The IR cut filter60prevents radiant heat, which is emitted from external light, from being transferred to the light receiving device400. In other words, the infrared cut filter60transmits visible light, and reflects infrared light so that the infrared light is discharged.

In addition, the light receiving device70, on which an image is formed, may include an image sensor to convert an optical signal, which corresponds to the image of an object, into an electrical signal, and the image sensor may include a CCD sensor or a CMOS sensor.

The small optical system according to the embodiment satisfies the following Equation 1.
1.5<n2<1.55
50<v2<70
20<v3<30  Equation 1

In Equation 1, n2represents a refractive index of the second lens20, v2represents an abbe number of the second lens20, and v3represents an abbe number of the third lens30.

In addition to Equation 1, the small optical system according to the embodiment may satisfy following equation 3.
0.8<f1/F<1.2  Equation 3

In Equation 3, f1represents an effective focus length of the first lens10, and F represents the whole effective focus length of the small optical system according to the embodiment.

In addition to Equations 1 and 3, the small optical system according to the embodiment may satisfy following Equation 4.
φ4>φ1>φ2  Equation 4

In Equation 4, φ1represents refractive power of the first lens10, φ2represents refractive power of the second lens20, and φ4represents refractive power of the fourth lens40.

Therefore, the small optical system according to the embodiment may satisfy following Equation 2.
1<tt1/F<1.3  Equation 2

In Equation 2, tt1represents a distance from the surface facing the object of the first lens10to the surface facing the image of the fifth lens on the optical axis of the lens system.

The optical system according to the embodiment represents lower tt1based on the whole effective focus length. In other words, the distance from the side R1of the first lens10facing the object side to a side R11of the fifth lens50facing the image side may represent a very small value.

Experimental Example

The small optical system according to the experimental example represents an optical characteristic shown in table 1.

The thickness marked in Table 1 represents a distance from each lens surface to a next lens surface.

Following table 2 shows aspheric surface coefficient of an aspheric lens according to the embodiment.

An aspheric surface coefficient of Table 2 for the aspheric lens according to the experimental example can be obtained from Equation 6.

Z: a distance from a vertex of a lens in an optical axis direction

C: a basic curvature of a lens

Y: a distance in a direction perpendicular to an optical axis

K: a conic constant

The aspheric shape for each lens according to the experimental example is determined as described above.

In addition, according to the experimental example, each lens is designed as shown in table 3.

When the small optical system according to the experimental example is designed as described above, the small optical system can represent performance shown in following table 4.

As described above, if the small optical system according to the experimental example satisfies Equation 1 and Equations 3 to 5, the values of tt1and F can be obtained in such a manner that the small optical system satisfies Equation 2.

Accordingly, the small optical system according to the embodiment is designed as shown in Equation 1 and Equations 3 to 5, so that the small optical system can represent improved performance and a small size.