KR20090047745A - Subminiature optical system - Google Patents

Abstract

Provides an ultra-small imaging optical system.

The first lens group includes a first lens arrangement having an aperture stop closest to the object side, and then in order from the object side to the front of the image, the object side surface is convex toward the object side and includes a first lens having positive refractive power; A second lens group having a second lens having a positive refractive power and a third lens having a negative refractive power, wherein an image side surface of the second lens and an object side surface of the third lens are bonded or separated from each other; A third lens group having a fourth lens having an image side surface convex toward the image side and having a positive refractive power; And a fourth lens group having a fifth lens having negative refractive power; It includes.

According to the present invention, high performance and compactness can be miniaturized, and resolution can be further improved, and chromatic aberration is also well corrected, so that color fringing in indoor or outdoor shots can be satisfactorily improved.

Optical system, lens, aspherical surface, refractive power, Abbe's number

Description

Subminiature Optical System

The present invention relates to an imaging optical system. More particularly, the present invention relates to an imaging optical system. More particularly, the present invention relates to an imaging optical system, which is compact and has a high resolution and is mounted on a mobile communication terminal, a PDA, or the like. It relates to an ultra-small imaging optical system that can be photographed easily.

In general, a camera module lens used in a mobile communication terminal is composed of two or three lenses in a low pixel class and three or four lenses in a high pixel class.

In other words, the lens employed in the camera module designed for the low pixel class can be composed of three lenses because the pixel size is relatively large and the resolution required on the screen is low, and in some cases, two lenses can be used. However, the lens employed in the camera module designed for the high pixel class is composed of three or four lenses because the pixel size is small and the resolution required on the screen is high.

When the imaging optical system is composed of three sheets, it is difficult to properly correct chromatic aberration. Therefore, by configuring the imaging optical system composed of four sheets, chromatic aberration correction can be facilitated and image quality can be improved.

Accordingly, the present invention is to solve the above problems, the purpose of which is high performance and compact to achieve a miniaturization, and to improve the resolution while also correcting the chromatic aberration (Chromatic Aberration) with good color bleeding in indoor or outdoor shooting (Color Fringing) It is an object of the present invention to provide an ultra-small imaging optical system that can improve the phenomenon well.

As a specific means for achieving the above object, the present invention provides a first aperture having the object stop on the object side convex toward the object side, in order from the object side to the front surface in order from the object aperture closest to the object side; A first lens group including a lens; A second lens group having a second lens having a positive refractive power and a third lens having a negative refractive power, wherein an image side surface of the second lens and an object side surface of the third lens are bonded or separated from each other; A third lens group having a fourth lens having an image side surface convex toward the image side and having a positive refractive power; And a fourth lens group having a fifth lens having negative refractive power; It provides a very small imaging optical system comprising a.

Preferably, at least one side of the fourth lens and the fifth lens included in the third lens group and the fourth lens group has an aspherical surface shape.

More preferably, the following Conditional Expression 1 is satisfied with respect to the optical axis direction dimension of the optical system.

(Condition 1) 1.0 <TL / f <1.5

Here, TL is the distance from the first lens object side surface of the first lens group to the image surface, and f is the focal length of the whole optical system.

More preferably, the following Conditional Expression 2 is satisfied with respect to the refractive power of the first lens group.

(Condition 2) 0.5 <f1 / f <1.0

Here, f1 'is the focal length of the first lens group.

More preferably, the following Conditional Expression 3 is satisfied with respect to the refractive power of the first and second lens groups.

(Condition 3) 1.1 <f12 / f <1.5

Here, f12 is a combined focal length of the first lens group and the second lens group.

More preferably, the following Conditional Expression 4 is satisfied with respect to the shape of the fourth lens.

(Condition 4) -2.5 <R_L4F / f <-1.0

Here, R_L4F is the radius of curvature of the object-side surface of the fourth lens.

More preferably, the following Conditional Expressions 5 and 6 are satisfied with respect to the Abbe number of the second and third lenses.

(Condition 5) 45 <V_L2 <71

(Condition 6) 23 <V_L3 <40

Where V_L2 is the Abbe's number of the second lens and V_L3 is the Abbe's number of the third lens.

More preferably, the following Conditional Expression 7 is satisfied with respect to the refractive power of the third lens group and the fourth lens group.

(Condition 7) -1.4 <f3 / f4 <-0.8

Here, f3 is the focal length of the third lens group and f4 is the focal length of the fourth lens group.

According to the present invention having the above-described configuration, there is an effect that a compact and ultra-compact optical system can be obtained with a high resolution and a small number of lenses.

Further, by correcting the chromatic aberration while improving the resolution, the color fringing phenomenon can be satisfactorily improved in indoor or outdoor photography, thereby improving quality and reliability.

In addition, by using a lens made of a plastic material, not only can be reduced in weight, but also has an advantageous effect that an optical system can be implemented, which is easy to manufacture, which enables mass production and low manufacturing cost.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1,3,5,7,9,11,13,15,17 and 19 are the first, second, third, fourth, fifth, sixth, seventh, eighth, nineth and tenth embodiments of the microscopic imaging optical system according to the present invention. It is a lens block diagram which shows the example. In the following lens configuration, the thickness, size, and shape of the lens have been somewhat exaggerated for explanation, and in particular, the shape of the spherical or aspherical surface shown in the lens configuration is merely an example and is not limited thereto.

As shown in Figs. 1, 3, 5, 7, 9, 11, 13, 15, 17 and 19, the embodiment of the present invention provides an aperture stop S for removing unnecessary light at the closest object side. And a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4 in order from the object side.

The first lens group G1 includes a first lens L1, and the first lens L1 has an object-side surface 1 convex toward the object side and has a positive refractive power.

The second lens group G2 includes a second lens L2 having a positive refractive power and a third lens L3 having a negative refractive power, and an image side surface 4 of the second lens L2. Although the object-side surface 5 of the third lens L3 is shown to be bonded to each other, it is not limited thereto and may be separated from each other.

The third lens group G3 includes a fourth lens L4, and the fourth lens L4 has an image surface 7 convex toward the image side and has a positive refractive power.

The fourth lens group G4 includes a fifth lens L5, and the fifth lens L5 has negative refractive power.

Herein, at least one of the object-side surfaces 6 and 8 and the image-side surfaces 7 and 9 may be provided as an aspheric surface of the fourth lens L4 and the fifth lens L5.

 In addition, by constructing two or more of the lenses provided in the first lens group G1 to the fourth lens group G4 with plastic lenses, the manufacturing cost is low, mass production is possible, and the advantages of small and light optical systems can be realized. have.

In addition, since the at least one surface of the fourth and fifth lenses L4 and L5 is aspheric, the optical system can be miniaturized compared to the spherical lens.

In addition, the fifth lens L5 of the fourth lens group G4 is provided with a cross section in which the image side surface 9 is convex toward the object side and convex toward the image as the image surface 9 moves away from the optical axis toward the periphery thereof. A curved point is formed on the upper surface 9 of the c).

The infrared filter IF is provided behind the fourth lens group G4. The infrared filter IF may be replaced or omitted with other filters as necessary, and shall not affect the optical properties of the present invention in principle.

In addition, the image sensor includes a Charged Coupled Device (CCD), a Complementarly Metal Oxide Semiconductor (CMOS), and the like, and corresponds to an upper surface (photosensitive surface) 12 that receives an image formed by a lens. It is arranged behind the infrared filter IF.

Look at the effect of the following Conditional Expressions 1 to 7 under such an overall configuration.

(Condition 1) 1.0 <TL / f <1.5

Here, TL is the distance from the object-side surface 1 of the first lens L1 to the image surface 12 of the first lens group G1.

Conditional Expression 1 is to reduce the overall length of the optical system while satisfying the high resolution, and when it is out of the lower limit, coma and astigmatism are largely generated, so that it is difficult to obtain a clear image, and the optimal top position of the screen center and surroundings is greatly increased. This makes it impossible to achieve high resolution across the screen. In addition, the pads synthesizing (Petzval) Sum) is increased, the upper surface curvature is increased. If the upper limit is out of the upper limit, the distance from the object-side surface 1 of the first lens L1 to the image surface 12 becomes long, which makes it difficult to design a compact optical system.

(Condition 2) 0.5 <f1 / f <1.0

Here, f1 is the focal length of the first lens group G1.

Condition 2 is to ensure excellent image quality by suppressing spherical aberration and coma flare generation while maintaining the refractive power of the first lens group and the overall size of the optical system small. The image quality is deteriorated. And, if the deviation from the upper limit, the refractive power of the first lens (L1) is weakened, so that the store location where the light rays starting from the object-side surface (1) of the first lens (L1) meets the optical axis is far away. It becomes difficult to get

(Condition 3) 1.1 <f12 / f <1.5

Here, f12 is the combined focal length of the first lens group G1 and the second lens group G2.

Conditional Expression 3 relates to the refractive power of the first and second lens groups G1 and G2, and is to maintain the overall size of the optical system while minimizing the occurrence of color fringing that may affect the image quality. If it is out of the lower limit, the position of the image point of each wavelength of the light beam incident toward one point of the image surface is greatly deviated, resulting in color bleeding, thereby degrading image quality. And, if the deviation from the upper limit, the force to refract the incident light flux is weakened, the distance from the object-side surface 1 of the first lens group G1 to the image surface 12 becomes long, so that the compact optical system It becomes difficult to get

(Condition 4) -2.5 <R_L4F / f <-1.0

Here, R_L4F is the radius of curvature of the object-side surface 6 of the fourth lens L4.

Conditional Expression 4 relates to the shape of the fourth lens (L1), and to minimize the shape distortion of the subject to reduce the overall size of the optical system, if the deviation from the lower limit, the symmetry of the optical system is broken, the distortion aberration becomes very large. If it is out of the upper limit, the distortion aberration can be made very small, but the shop position is moved backwards, so that the distance from the object side surface 1 of the first lens L1 to the image surface 12 becomes farther, and thus the length of the entire photographing lens system Becomes large.

(Condition 5) 45 <V_L2 <71

(Condition 6) 23 <V_L3 <40

Here, V_L2 is the Abbe's number of the second lens, and V_L3 'is the Abbe's number of the third lens.

Conditional Expressions 5 and 6 relate to Abbe's numbers of the second and third lenses L2 and L3. When this is satisfied, the chromatic aberration generated by the second lens L2 having positive refractive power is negative. Correction can be appropriately performed by the three lenses L3.

(Condition 7) -1.4 <f3 / f4 <-0.8

Here, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4.

Condition 7 relates to the angle of the chief ray angle incident on the upper surface 12. In an optical system using an image sensor such as a CMOS or a CCD, a microlens array on an image sensor surface is formed to obtain good light sensitivity. By properly arranging the micro lens array, the incident angle of the chief rays of light is increased, whereby the chief rays of incidence of the image sensor with good light sensitivity are determined.

Therefore, when the conditional expression 7 is out of the range, the light receiving sensitivity of the image sensor is sharply deteriorated, thereby degrading or darkening the image quality.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

The aspherical surface used in each of the following examples is obtained from well-known Equation 1, and is used for the Conic constant (K) and the aspherical coefficients (A, B, C, D, and E), followed by the numerals. 'Represents a power of 10. For example, E21 has a 10 ^21, E-02 indicates the ^10-2.

Z (r): Distance from the vertex of the lens to the optical axis direction

r: distance in the direction perpendicular to the optical axis

c: radius of curvature at the vertex of the lens

K: Conic constant

A, B, C, D, E, F: Aspherical Coefficient

Example 1

Table 1 below shows numerical examples according to the first embodiment of the present invention.

1 is a lens configuration diagram showing a miniature imaging optical system according to a first embodiment of the present invention, and FIGS. 2A to 2C show aberrations of the optical systems shown in Table 1 and FIG. 1.

In addition, the d line shown in the spherical aberration diagram below shows a 587.56 nm wavelength, the g line shows a 435.83 nm wavelength, the c line shows 656.27 nm, and S.C is a sine condition. In the astigmatism diagram, "S" represents sagittal and "M" represents tangential.

In Example 1, the effective focal length f of the entire lens system is 5.686 mm, the F number F _No is 2.8, and the total angle of the lens (2ω) is 64 °. The total length TL from the object-side surface of the first lens group to the image surface is 6.50 mm.

The focal length f1 of the first lens group G1 is 3.74 mm, the focal length f2 of the second lens group G2 is -5.238 mm, and the focal length f3 of the third lens group G3 is 3.735. mm, and the focal length f4 of the fourth lens group G4 is −3.169 mm.

In Table 1, * denotes an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 2 below.

Example 2

Table 3 below shows a numerical example according to the second embodiment of the present invention.

4 is a lens configuration diagram illustrating a microscopic imaging optical system according to a second exemplary embodiment of the present invention, and FIGS. 4A to 4C show aberrations of the optical systems shown in Tables 3 and 3.

In Example 2, the effective focal length f of the optical system is 5.683 mm, the F number F _No is 2.8, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface to the image surface of one lens group is 6.50 mm.

The focal length f1 of the first lens group G1 is 3.651 mm, the focal length f2 of the second lens group G2 is -5.538 mm, and the focal length f3 of the third lens group G3 is 4.070. mm, and the focal length f4 of the fourth lens group G4 is −3.523 mm.

In Table 3, * represents an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 4 below.

Example 3

Table 5 below shows a numerical example according to the third embodiment of the present invention.

6 is a lens configuration diagram showing a microscopic imaging optical system according to a third exemplary embodiment of the present invention, and FIGS. 6A to 6C show aberrations of the optical systems shown in Tables 5 and 5.

In Example 3, the effective focal length f of the optical system is 5.699 mm, the F number F _No is 2.8, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface to the image surface of one lens group is 6.80 mm.

The focal length f1 of the first lens group G1 is 3.554 mm, the focal length f2 of the second lens group G2 is -5.029 mm, and the focal length f3 of the third lens group G3 is 2.776. mm, and the focal length f4 of the fourth lens group G4 is -2.646 mm.

In Table 5, * represents an aspherical surface, and the values of the koenic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 6 below.

Example 4

Table 7 below shows numerical examples according to the fourth embodiment of the present invention.

7 is a lens configuration diagram illustrating a microscopic imaging optical system according to a fourth exemplary embodiment of the present invention, and FIGS. 8A to 8C illustrate aberrations of the optical systems shown in Tables 7 and 7.

In Example 4, the effective focal length f of the optical system is 5.700 mm, the F number F _No is 2.8, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface to the image surface of one lens group is 6.80 mm.

The focal length f1 of the first lens group G1 is 3.430 mm, the focal length f2 of the second lens group G2 is -4.851 mm, and the focal length f3 of the third lens group G3 is 2.714. mm, and the focal length f4 of the fourth lens group G4 is -2.545 mm.

In Table 7, * represents an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 8 below.

Example 5

Table 9 below shows a numerical example according to the fifth embodiment of the present invention.

9 is a lens configuration diagram illustrating a microscopic imaging optical system according to a fifth exemplary embodiment of the present invention, and FIGS. 10A to 10C show aberrations of the optical systems shown in Tables 9 and 9.

In Example 5, the effective focal length f of the optical system is 5.706 mm, the F number F _No is 2.6, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface of the one lens group to the image surface is 7.15 mm.

The focal length f1 of the first lens group G1 is 3.551 mm, the focal length f2 of the second lens group G2 is -5.332 mm, and the focal length f3 of the third lens group G3 is 2.311. mm, and the focal length f4 of the fourth lens group G4 is -2.195 mm.

In Table 9, * represents an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 10 below.

Example 6

Table 11 below shows a numerical example according to the sixth embodiment of the present invention.

11 is a lens configuration diagram showing a microscopic imaging optical system according to a sixth embodiment of the present invention, and FIGS. 12A to 12C show aberrations of the optical systems shown in Tables 11 and 11.

In Example 6, the effective focal length f of the optical system was 5.691 mm, the F number F _No was 2.6, and the total angle 2ω of the lens was 64 °. The total length TL from the object-side surface of the one lens group to the image surface is 7.15 mm.

The focal length f1 of the first lens group G1 is 3.586 mm, the focal length f2 of the second lens group G2 is -5.274 mm, and the focal length f3 of the third lens group G3 is 2.697. mm, and the focal length f4 of the fourth lens group G4 is -2.608 mm.

In Table 11, * represents an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 12 below.

Example 7

Table 13 below shows a numerical example according to the seventh embodiment of the present invention.

13 is a lens configuration diagram showing a miniature imaging optical system according to a seventh embodiment of the present invention, and FIGS. 14A to 14C show aberrations of the optical systems shown in Tables 13 and 13.

In Example 7, the effective focal length f of the optical system is 5.698 mm, the F number F _No is 2.6, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface to the image surface of one lens group is 7.58 mm.

The focal length f1 of the first lens group G1 is 4.434 mm, the focal length f2 of the second lens group G2 is -7.478 mm, and the focal length f3 of the third lens group G3 is 2.652. mm, and the focal length f4 of the fourth lens group G4 is -2.599 mm.

In Table 13, * represents an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 14 below.

Example 8

Table 15 below shows numerical examples according to the eighth embodiment of the present invention.

15 is a lens configuration diagram showing a microscopic imaging optical system according to an eighth embodiment of the present invention, and FIGS. 16A to 16C show aberrations of the optical systems shown in Tables 15 and 15. FIG.

In Example 8, the effective focal length f of the optical system is 5.702 mm, the F number F _No is 2.6, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface to the image surface of one lens group is 7.58 mm.

The focal length f1 of the first lens group G1 is 4.460 mm, the focal length f2 of the second lens group G2 is -7.334 mm, and the focal length f3 of the third lens group G3 is 2.612. mm, and the focal length f4 of the fourth lens group G4 is -2.554 mm.

In Table 15, * represents an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 16 below.

Example 9

Table 17 below shows a numerical example according to the ninth embodiment of the present invention.

17 is a lens configuration diagram showing a microscopic imaging optical system according to a ninth embodiment of the present invention, and FIGS. 18A to 18C show aberrations of the optical systems shown in Table 17 and FIG.

In Example 9, the effective focal length f of the optical system is 5.701 mm, the F number F _No is 2.6, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface of the one lens group to the image surface is 7.92 mm.

The focal length f1 of the first lens group G1 is 4.972 mm, the focal length f2 of the second lens group G2 is -9.728 mm, and the focal length f3 of the third lens group G3 is 2.706. mm, and the focal length f4 of the fourth lens group G4 is -2.624 mm.

In Table 17, * represents an aspherical surface, and the values of the koenic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 18 below.

Example 10

Table 19 below shows a numerical example according to the tenth embodiment of the present invention.

20 is a lens configuration diagram illustrating a microscopic imaging optical system according to a tenth embodiment of the present invention, and FIGS. 20A to 20C show aberrations of the optical systems shown in Table 19 and FIG. 19.

In Example 10, the effective focal length f of the optical system is 5.698 mm, the F number F _No is 2.6, and the total angle 2ω of the lens is 64 °. The total length TL from the object-side surface to the image surface of one lens group is 7.94 mm.

The focal length f1 of the first lens group G1 is 4.606 mm, the focal length f2 of the second lens group G2 is -7.395 mm, and the focal length f3 of the third lens group G3 is 2.504. mm, and the focal length f4 of the fourth lens group G4 is -2.443 mm.

In Table 19, * represents an aspherical surface, and the values of the conic constant (K) and aspherical coefficients (A, B, C, D, E, and F) according to Equation 1 are shown in Table 20 below.

The values of Conditional Expressions 1 to 7 for Examples 1 to 10 are shown in Table 21 below.

As shown in Table 21, Examples 1 to 10 of the present invention satisfy conditional expressions 1 to 7, and FIGS. 2, 4, 6, 8, 10, 12, 14, 16, and FIG. As shown in FIG. 18 and FIG. 20, it can be seen that an optical system having excellent characteristics of the aberration is implemented.

1 is a lens diagram illustrating a microscopic imaging optical system according to a first exemplary embodiment of the present invention.

2A to 2C are graphs illustrating aberrations of the optical system illustrated in FIG. 1.

3 is a lens diagram illustrating a microscopic imaging optical system according to a second exemplary embodiment of the present invention.

4A to 4C are graphs showing aberrations of the optical system illustrated in FIG. 3.

5 is a lens diagram illustrating a microscopic imaging optical system according to a third exemplary embodiment of the present invention.

6A to 6C are graphs illustrating aberrations of the optical system illustrated in FIG. 5.

7 is a lens diagram illustrating a microscopic imaging optical system according to a fourth embodiment of the present invention.

8A to 8C are graphs illustrating aberrations of the optical system illustrated in FIG. 7.

9 is a lens diagram illustrating a microscopic imaging optical system according to a fifth exemplary embodiment of the present invention.

10A to 10C are graphs illustrating aberrations of the optical system illustrated in FIG. 9.

11 is a lens diagram illustrating a microscopic imaging optical system according to a sixth embodiment of the present invention.

12A to 12C are graphs illustrating aberrations of the optical system illustrated in FIG. 11.

13 is a lens configuration diagram illustrating a microscopic imaging optical system according to a seventh exemplary embodiment of the present invention.

14A to 14C are graphs showing aberrations of the optical system shown in FIG. 13.

15 is a lens configuration diagram illustrating a microscopic imaging optical system according to an eighth embodiment of the present invention.

16A to 16C are graphs showing aberrations of the optical system shown in FIG. 15.

17 is a lens diagram illustrating a microscopic imaging optical system according to a ninth embodiment of the present invention.

18A to 18C are graphs showing aberrations of the optical system shown in FIG. 17.

19 is a lens diagram illustrating a microscopic imaging optical system according to a tenth embodiment of the present invention.

20A to 20C are graphs illustrating aberrations of the optical system illustrated in FIG. 19.

Explanation of symbols on the main parts of the drawings

G1: first lens group G2: second lens group

G2: second lens group G4: fourth lens group

L1: first lens L2: second lens

L3: third lens L4: fourth lens

L5: 5th lens S ...

Claims (14)

Place the aperture stop closest to the object side and then in sequence from the object side to the front face, A first lens group having a first lens having an object-side surface convex toward the object side and having a positive refractive power; A second lens group having a second lens having a positive refractive power and a third lens having a negative refractive power, wherein an image side surface of the second lens and an object side surface of the third lens are bonded or separated from each other; A third lens group having a fourth lens having an image side surface convex toward the image side and having a positive refractive power; And A fourth lens group including a fifth lens having negative refractive power; Miniature imaging optical system comprising a. The ultra-small imaging optical system of claim 1, wherein at least one side of the fourth lens and the fifth lens included in the third lens group and the fourth lens group has an aspherical surface shape. The ultra-small imaging optical system according to claim 2, wherein the following Conditional Expression 1 is satisfied with respect to the optical axis direction dimension of the optical system. (Condition 1) 1.0 <TL / f <1.5 TL: distance from the first lens object side surface of the first lens group to the image surface f: focal length of the whole optical system The ultra-small imaging optical system according to claim 2, wherein the following conditional expression 2 is satisfied with respect to the refractive power of the first lens group. (Condition 2) 0.5 <f1 / f <1.0 Where f1 is the focal length of the first lens group. The ultra-compact optical system according to claim 2, wherein the following conditional expression 3 is satisfied with respect to the refractive power of the first and second lens groups. (Condition 3) 1.1 <f12 / f <1.5 Where f12 is the combined focal length of the first lens group and the second lens group. The ultra-small imaging optical system according to claim 2, wherein the following conditional expression 4 is satisfied with respect to the shape of the fourth lens. (Condition 4) -2.5 <R_L4F / f <-1.0 Where R_L4F is the radius of curvature of the object-side surface of the fourth lens. The ultra-small imaging optical system according to claim 2, wherein the following Conditional Expressions 5 and 6 are satisfied with respect to the Abbe number of the second and third lenses. (Condition 5) 45 <V_L2 <71 (Condition 6) 23 <V_L3 <40 Where V_L2 is the Abbe number of the second lens. V_L3: Abbe number of the third lens The ultra-small imaging optical system according to claim 2, wherein the following conditional expression 7 is satisfied with respect to the refractive power of the third lens group and the fourth lens group. (Condition 7) -1.4 <f3 / f4 <-0.8 Where f3 is the focal length of the first lens group. f4: The focal length of the fourth lens group Place the aperture stop closest to the object side and then in sequence from the object side to the front face, A first lens group having a first lens having an object-side surface convex toward the object side and having a positive refractive power; A second lens group having a second lens having a positive refractive power and a third lens having a negative refractive power, wherein an image side surface of the second lens and an object side surface of the third lens are bonded or separated from each other; A third lens group having an image side surface convex toward the image side, at least one side surface being provided as an aspherical surface, and having a fourth lens having positive refractive power; And A fourth lens group having at least one side as an aspherical surface and having a fifth lens having negative refractive power; Including, The optical imaging system according to claim 1, wherein the following conditional expression 1 is satisfied with respect to the optical axis direction dimension of the optical system, and the following conditional expression 2 is satisfied with respect to the refractive power of the first lens. (Condition 1) 1.0 <TL / f <1.5 (Condition 2) 0.5 <f1 / f <1.0 TL: distance from the first lens object side surface of the first lens group to the image surface f: focal length of the whole optical system f1: The focal length of the first lens 10. The microscopic optical system according to claim 9, wherein the following conditional expression 3 is satisfied with respect to the refractive power of the first and second lens groups. (Condition 3) 1.1 <f12 / f <1.5 Where f12 is the combined focal length of the first lens group and the second lens group. Place the aperture stop closest to the object side and then in sequence from the object side to the front face, A first lens group having a first lens having an object-side surface convex toward the object side and having a positive refractive power; A second lens group having a second lens having a positive refractive power and a third lens having a negative refractive power, wherein an image side surface of the second lens and an object side surface of the third lens are bonded or separated from each other; A third lens group having an image side surface convex toward the image side, at least one side surface being provided as an aspherical surface, and having a fourth lens having positive refractive power; And A fourth lens group having at least one side as an aspherical surface and having a fifth lens having negative refractive power; Including, A miniature imaging optical system, wherein the following Conditional Expression 1 is satisfied with respect to the optical axis direction dimension of the optical system. (Condition 1) 1.0 <TL / f <1.5 TL: distance from the first lens object side surface of the first lens group to the image surface f: focal length of the whole optical system 12. The microscopic imaging optical system of claim 11, wherein the fifth lens of the fourth lens group has a curved point on an image side surface. Place the aperture stop closest to the object side and then in sequence from the object side to the front face, A first lens group having a first lens having an object-side surface convex toward the object side and having a positive refractive power; A second lens group having a second lens having a positive refractive power and a third lens having a negative refractive power, wherein an image side surface of the second lens and an object side surface of the third lens are bonded or separated from each other; A third lens group having an image side surface convex toward the image side, at least one side surface being provided as an aspherical surface, and having a fourth lens having positive refractive power; And A fourth lens group having at least one side as an aspherical surface and having a fifth lens having negative refractive power; Miniature imaging optical system comprising a. The microscopic image pickup optical system according to claim 13, wherein the fifth lens of the fourth lens group is provided in a cross section in which an image side surface is convex toward an object which can be moved away from the optical axis, and is convex toward the image side surface.

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