JP2858639B2 - Wide-angle lens for UV - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet lens for use in an ultraviolet image pickup device, and more particularly to an ultraviolet wide-angle lens used in a wavelength band longer than 0.20 .mu.m.

[0002]

2. Description of the Related Art Conventional wide-angle lenses are disclosed, for example, in JP-A-54-137328 and JP-A-55-164.
No. 805 and JP-A-58-58514 disclose 1
A single-focus wide-angle lens including a cemented lens with a zero-element configuration is disclosed.

[0003]

However, Japanese Patent Application Laid-Open Nos. Sho 54-137328 and 55-164 describe above.
No. 805 and Japanese Patent Application Laid-Open No. 58-58514.
When trying to achieve a single focus lens with the specifications of
The aberration cannot be corrected well, and a clear image cannot be obtained. Further, the lens configuration disclosed in the above publication has a problem in that it is not possible to sufficiently secure a space for disposing a plurality of ND filters and polarizing filters that can be inserted and removed between the lenses.

The present invention has been made in view of the above problems, and has as its object the purpose of the present invention.
For ultraviolet rays in a wavelength band longer than m, achieves a full angle of view of 120 degrees, has a bright F-number of 1.2, and provides space for multiple ND filters and polarizing filters that can be inserted and removed between lenses. It is an object of the present invention to provide a wide-angle lens for an ultraviolet ray which can sufficiently secure, further, can secure a sufficient back focus, and has good imaging performance.

[0005]

In order to achieve the above object, a wide-angle lens for ultraviolet rays according to the present invention has the following construction. For example, as shown in FIG. 1, the wide-angle lens for ultraviolet light of the present invention is a wide-angle lens for ultraviolet light having a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power in order from the object side. The first lens group G1 includes, in order from the object side, a first lens group having a negative refractive power with a convex surface facing the object side.
The second lens group G having a lens component L1 and a second lens component L2 having a negative refractive power with the convex surface facing the object side;
Reference numeral 2 denotes, in order from the object side, a third lens component L3 having a positive refractive power with a concave surface facing the object side, a fourth lens component L4 having a negative refractive power, and a fifth lens component having a positive refractive power. L5, a sixth lens component L6 having a negative refractive power,
A seventh lens component L7 having a positive refractive power, an eighth lens component L8 having a negative refractive power, a ninth lens component L9 having a negative refractive power with the concave surface facing the object side, and a positive refractive power. And a tenth lens component L10. The wide-angle lens for ultraviolet light according to the present invention is configured to satisfy the following conditions. 1.86 <| f1 / fT | <1.89 (1) 3.00 <| f2 / fT | <3.22 (2) where f1: focal point of the first lens group G1 Distance, fT: focal length of the entire system, f2: focal length of the second lens group G2.

According to a preferred embodiment of the ultraviolet wide-angle lens according to the present invention, the distance between the second lens component L2 and the third lens component L3 on the optical axis is D1, and the total focal point of the ultraviolet wide-angle lens. Assuming that the distance is fT, 2.7 <| D1 / fT | <2.9 (3) is satisfied.

According to another preferred embodiment of the ultraviolet wide-angle lens according to the present invention, the radius of curvature of the object-side lens surface of the ninth lens component L9 is r21, and the focal length of the ultraviolet wide-angle lens is fT. At this time, −6.0 <r21 / fT <−3.0 (4) is satisfied.

[0008]

Embodiments of the present invention are described below.
The description will be made assuming that the present invention is applied as an optical system for a so-called ultraviolet imaging device that obtains an ultraviolet image by using ultraviolet light in a wavelength band of 0.28 to 0.3 μm.

FIG. 1 is a lens configuration diagram of a wide-angle lens for ultraviolet light according to an embodiment of the present invention. In FIG. 1, a wide-angle lens for ultraviolet rays has a first negative refractive power in order from the object side.
It comprises a lens group G1 and a second lens group G2 having a positive refractive power.

The first negative lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side as a first lens component of negative refractive power having a convex surface facing the object side.
And a negative meniscus lens L2 having a convex surface facing the object side as a second lens component of negative refractive power having a convex surface facing the object side.

The second positive lens group G2 includes, in order from the object side, a positive meniscus lens L having a concave surface facing the object side as a third lens component of positive refractive power having a concave surface facing the object side.
3, a negative meniscus lens L4 having a convex surface directed to the object side as a fourth lens component having a negative refractive power, a biconvex positive lens L5 serving as a fifth lens component having a positive refractive power, and a negative meniscus lens L5 having a negative refractive power. A negative meniscus lens L6 having a concave surface facing the object side as a six-lens component, a biconvex positive lens L7 as a seventh lens component with a positive refractive power, and an object side as an eighth lens component with a negative refractive power Negative meniscus lens L with concave surface
8, a negative meniscus lens L9 having a concave surface facing the object side as a ninth lens component of negative refractive power having a concave surface facing the object side
And a meniscus lens L10 having a convex surface facing the object side as a tenth lens component having a positive refractive power.

FIG. 3 is a lens configuration diagram of a wide-angle lens for ultraviolet light according to another embodiment of the present invention. The wide-angle lens for ultraviolet light shown in FIG. 3 has the same configuration as the wide-angle lens for ultraviolet light shown in FIG.

In the embodiment shown in FIGS. 1 and 3, the first
A filter F is provided between the lens group G1 and the second lens group G2.
Is arranged. FIGS. 1 and 3 also show a window W that is disposed between the second lens group G2 and the image plane I where the surface of the ultraviolet detector is located and protects the surface of the ultraviolet detector. ing.

The wide-angle lens for ultraviolet light shown in FIGS. 1 and 3 satisfies the following conditions. 1.86 <| f1 / fT | <1.89 (1) 3.00 <| f2 / fT | <3.22 (2) where f1: focal point of the first lens group G1 Distance, fT: focal length of the entire system, f2: focal length of the second lens group G2.

As described above, the wide-angle lens for ultraviolet light according to the embodiment of the present invention includes ten lenses in ten groups, and the focal length between the first negative lens group G1 and the second positive lens group G2. Is defined within an appropriate range, the F-number is 1.times. Without deteriorating various aberrations.
2, a lens with an angle of view of 120 degrees can be realized. With the above-described configuration, in the ultraviolet wide-angle lens according to the embodiment of the present invention, a plurality of ND filters, polarizing filters, and the like that can be inserted and removed between the first negative lens group G1 and the second positive lens group G2 are provided. Space for arrangement can be secured. Hereinafter, the above conditions will be described in detail.

The condition (1) defines an optimum ratio of the focal length of the first lens group G1. If the value exceeds the upper limit of the condition (1), the first lens group G1
Becomes weak, and it becomes impossible to obtain a long back focus. If the value exceeds the upper limit of the condition (1), the diameter of the front lens must be extremely large in order to transmit a light beam over an entire angle of view of 120 degrees, which is not preferable.

On the other hand, if the lower limit of the condition (1) is exceeded, the refracting power of the first lens group G1 becomes strong, so that the back focus can be lengthened.
Various aberrations such as coma, astigmatism, and distortion are significantly generated, and the second lens group G2 cannot correct these various aberrations, which is not preferable.

In order to further improve the optical performance of the wide-angle lens for ultraviolet light according to the embodiment of the present invention, it is desirable to set the upper limit of the above condition (1) to 1.88.

In the wide-angle lens for ultraviolet light according to the embodiment of the present invention, the second lens group G2 disposed following the first lens group G1 converges the luminous flux diverged by the first lens group G1. Has a role. The condition (2) is
The focal length f2 of the second lens group and the focal length fT of the entire system
And an appropriate focal length ratio of
This is to suppress the occurrence of various aberrations due to the passage of a light beam having the brightness of.

When the value exceeds the upper limit of the condition (2), the refractive power of the second lens unit becomes weak, so that it is difficult to correct off-axis astigmatism and coma generated in the first lens unit G1. Is not preferred. On the other hand, when the value exceeds the lower limit value of the condition (2), the refractive power of the second lens group G2 increases, so that not only the back focus is shortened, but also
This is not preferable because the diameter of the front lens becomes large. In this case, it is difficult to correct various aberrations such as spherical aberration and astigmatism.

The wide-angle lens for ultraviolet light according to the embodiment of the present invention includes a second lens component L2 and a third lens component L.
Assuming that the distance on the optical axis with respect to D3 is D1 and the focal length of the entire system is fT, the following condition is satisfied: 2.7 <| D1 / fT | <2.9 (3) Is desirable.

The condition (3) is to appropriately define the ratio of the distance between the second lens component L2 and the third lens component L3 on the optical axis with respect to the focal length of the entire system. In particular, this is a condition for securing a space for arranging a plurality of ND filters, polarizing filters, and the like so as to be freely inserted and removed while maintaining good optical performance. If the value exceeds the upper limit of the condition (3), the balance between the on-axis ray and the off-axis ray passing through the third lens component L3 becomes poor, and off-axis coma aberration largely occurs. Not preferred. In this case, it is not preferable because it becomes difficult to secure a necessary back focus.

On the other hand, when the value exceeds the lower limit of the condition (3), it means that the distance between the second lens component L2 and the third lens component L3 on the optical axis becomes small, and an ND filter, a polarizing filter, etc. Is not only difficult to arrange, but also causes coma and astigmatism.

The ultraviolet wide-angle lens according to the embodiment of the present invention has a ninth lens component L9 having a radius of curvature of the object-side lens surface of r21 and a focal length of the entire optical system of fT.
In this case, it is preferable to satisfy the following condition: -6.0 <r21 / fT <-3.0 (4)

The condition (4) defines the radius of curvature r21 of the ninth lens component L9 on the object-side lens surface to be an appropriate value, whereby the balance of spherical aberration, astigmatism, coma and the like is obtained. This is for correcting so as to be better.

When the value exceeds the upper limit of the condition (4), the radius of curvature r21 of the object-side lens surface of the ninth lens component L9 becomes large, so that the negative refractive power of this lens surface becomes weak. This is not preferable because not only negative spherical aberration occurs but also the curvature of field increases. On the other hand, condition (4)
If the value is below the lower limit of the above, it is not preferable because coma aberration and field curvature occur.

[0027]

EXAMPLES Tables 1 and 2 show numerical examples of the wide-angle lens for ultraviolet rays according to the embodiments of the present invention.

The following numerical examples show an example in which a wide-angle lens for ultraviolet light is applied as an optical system for a so-called ultraviolet image pickup device for obtaining an ultraviolet image with ultraviolet light in a wavelength band of 0.28 to 0.3 μm. is there.

The values of various numerical examples will be described below.
In Tables 1 and 2, fT is the focal length of the entire system with respect to ultraviolet rays having a wavelength of 0.29 μm, FNO is the open F number,
2ω represents the angle of view, and Bf represents the back focus. Also, f
1 represents the focal length of the first lens group, and f2 represents the focal length of the second lens group. The numbers at the left end indicate the order along the order of incidence of light rays, r indicates the radius of curvature of the lens surface, d indicates the distance between the lens surfaces, and n indicates the refractive index of each optical member with respect to ultraviolet rays of 0.29 μm. In the following Table 1 and Table 2, the data of the parallel flat plate corresponding to the filter F and the data of the parallel flat plate corresponding to the protection window W for the ultraviolet detector are also shown.

Next, Table 3 below shows the refractive index (n290, n280, n300) of each of the synthetic quartz and fluorite used as the lens material in the numerical examples. Here, n290 represents a refractive index for ultraviolet rays having a wavelength of 0.29 μm, n280 represents a refractive index for ultraviolet rays having a wavelength of 0.28 μm, and n300 represents a refractive index for ultraviolet rays having a wavelength of 0.3 μm.

[Table 3]

Next, FIGS. 2A and 2B show various aberration diagrams of the first embodiment at infinity, and FIGS. 4A and 4B show various aberration diagrams of the second embodiment at infinity. Here, in the spherical aberration diagram, the solid line indicates the aberration with respect to the ultraviolet ray having the wavelength of 0.29 μm, the dashed line indicates the aberration with respect to the ultraviolet ray having the wavelength of 0.28 μm,
The two-dot chain line indicates the aberration with respect to ultraviolet light having a wavelength of 0.3 μm, and the broken line indicates the sine condition. In the astigmatism diagram, a broken line indicates a meridional image plane for ultraviolet rays having a wavelength of 0.29 μm, and a solid line indicates a sagittal image plane for ultraviolet rays having a wavelength of 0.29 μm. In the coma diagram, the solid line indicates a meridional coma, and the broken line indicates a sagittal coma.

From the comparison of the aberration diagrams, it can be seen that the wide-angle lens for ultraviolet light according to each numerical example shows good optical performance over the wavelength range of 0.28 to 0.3 μm.
Table 4 below shows a condition correspondence value table of each embodiment according to the present invention.

[Table 4]

As described above, each embodiment according to the present invention satisfies the range defined by the above conditions.
Good imaging performance is achieved.

As described above, according to the embodiment of the present invention, as shown in the numerical examples, the ND filter which has a bright F-number of 1.2, has a wide angle of view, and can be inserted into and removed from the lens. A space for arranging a plurality of polarizing filters and the like can be ensured, and a wide-angle lens for ultraviolet rays with sufficiently corrected aberration can be provided with good optical performance.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment that is a numerical embodiment of the present invention.

FIG. 2 is a diagram illustrating various aberrations at infinity of a first embodiment that is a numerical embodiment of the present invention.

FIG. 3 is a lens configuration diagram of a second embodiment that is a numerical embodiment of the present invention.

FIG. 4 is a diagram illustrating various aberrations at infinity of a second embodiment that is a numerical embodiment of the present invention.

[Explanation of symbols]

 G1 first lens group G2 second lens group L1 first lens component L2 second lens component L3 third lens component L4 fourth lens component L5 fifth lens component L6 sixth lens component L7 seventh lens component L8 eighth lens component L9 9th lens component L10 10th lens component

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (3)

(57) [Claims] 1. An ultraviolet wide-angle lens having, in order from an object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, wherein the first lens group G1 is arranged in order from the object side. A first lens component having a negative refractive power with a convex surface facing the object side, and a second lens component having a negative refractive power with a convex surface facing the object side. The second lens group G2 is arranged from the object side. A third lens component having a positive refractive power with the concave surface facing the object side, a fourth lens component having a negative refractive power, a fifth lens component having a positive refractive power, and having a negative refractive power in order. A sixth lens component, a seventh lens component having a positive refractive power, an eighth lens component having a negative refractive power, a ninth lens component having a negative refractive power with a concave surface facing the object side, Consists of a tenth lens component having a refractive power, and satisfies the following conditions. A wide-angle lens for ultraviolet light characterized by addition. 1.86 <| f1 / fT | <1.89 3.00 <| f2 / fT | <3.22 where f1: focal length of the first lens group G1, fT: focal length of the entire system, f2: Focal length of the second lens group G2. 2. When the distance between the second lens component and the third lens component on the optical axis is D1, and the total focal length of the wide-angle lens for ultraviolet light is fT, 2.7 <| D1 / fT. The wide-angle lens for ultraviolet rays according to claim 1, wherein the following condition is satisfied: | <2.9. 3. Assuming that the radius of curvature of the object-side lens surface of the ninth lens component is r21 and the focal length of the ultraviolet wide-angle lens is fT, -6.0 <r21 / fT <-3.0. 3. The wide-angle lens for ultraviolet light according to claim 1, wherein the lens is satisfied.