JPH06242369A - Lens system for amphibian camera - Google Patents

Abstract

PURPOSE:To provide an amphibian lens system capable of obtaining effective description performance in both of air and water only by arranging two lenses in the front of a lens system whose aberration is effectively corrected in air. CONSTITUTION:The lens system is constituted of the 1st lens, the 2nd lens and a succeeding lens group arranged from the object side and the 1st and 2nd lenses have positive and negative or negative and positive refractive indexes and satisfies the following conditional expressions. Namely 10<nuP-nuN<60. 0.7<¦fN/fP¦<1.3 Provided that nuP and nuN is the Abbe numbers of the lenses having positive and negative refractive indexes out of the 1st and 2nd lenses and fP and fN are the focal distances of the lenses having positive and negative refractive indexes out of the 1st and 2nd lenses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens system for an amphibious camera which enables underwater photography as well as ordinary photography in the atmosphere.

[0002]

2. Description of the Related Art Various optical systems for underwater photographing cameras have been proposed in the past, and in many cases, an off-the-shelf optical system provided with a plane parallel plate for airtightness on the object side is used. The optical system formed in this way has the advantage of a simple structure because it is provided with a plane-parallel plate only. However, in general, a lens system with good aberration correction in air is used. Since the plane-parallel plate is arranged on the object side, when this optical system is used in water, chromatic aberration, particularly lateral chromatic aberration, is largely generated due to the chromatic dispersion of water, and the rendering performance is significantly deteriorated.

Further, as a system in which an optical system other than the plane-parallel plate is provided on the object side of the lens system, there is one disclosed in Japanese Patent Publication No. 3-56606. However, looking at the example, only one lens having a small refracting power is arranged on the object side of the lens system in which the aberration correction is substantially good in the air, so that the chromatic aberration of magnification when used in water is small. Has not been corrected, and therefore the underwater depiction performance is not good.

[0004]

SUMMARY OF THE INVENTION According to the present invention, by simply providing two lenses in front of an off-the-shelf lens system that has been satisfactorily corrected for aberrations in air, good drawing performance can be obtained both in air and in water. It seeks to provide amphibious lenses.

[0005]

The above object is composed of, from the object side, a first lens, a second lens, and a subsequent lens group, and the first lens and the second lens are respectively
Lens systems for amphibious cameras characterized by satisfying the following conditional expressions having refractive powers of opposite signs. 10 <ν _P −ν _N <60 (1) 0.7 <| f _N / f _P │ <1.3 (2) where ν _P : Abbe number of the first lens or the second lens having a positive refractive power ν _N : The negative refractive power of the first lens or the second lens Abbe number of lens f _P : focal length of the first lens or the second lens having a positive refractive power f _N : focal length of the first lens or the second lens having a negative refractive power Achieved by

[0006]

[Function] If a lens system that has been color-corrected in air is used as it is in water, chromatic aberration, especially lateral chromatic aberration, occurs greatly due to the color dispersion of water, and the depiction performance in water is extremely poor. become. In order to satisfactorily correct lateral chromatic aberration in water, a negative lens made of a glass material having a relatively large dispersion may be arranged in front of a lens system that has been chromatically corrected in air. However, if only the negative lens is arranged in front of the ready-made lens system in which various aberrations are well corrected in the air, the back focus becomes longer and the lens system becomes larger than before the negative lens is arranged. Aberrations in the air change remarkably, deteriorating the drawing performance.

In the present invention, a negative lens made of a glass material having a relatively large dispersion and a positive lens made of a glass material having a relatively small dispersion are arranged in front of a lens system in which various aberrations are well corrected in air. By doing so, the chromatic aberration of magnification in water is corrected well, and the chromatic aberration of magnification in water is satisfactorily corrected without increasing the size of the lens system and changing various aberrations other than chromatic aberration in air. It is to get performance.

The conditional expression of the present invention will be described below:
Conditional expression (1) defines the Abbe number of the glass material of the front two lenses, and is intended to favorably correct the chromatic aberration in air and water. If the lower limit of this equation is exceeded, lateral chromatic aberration cannot be corrected well in water. vice versa,
If the upper limit of this expression is exceeded, lateral chromatic aberration in air will deteriorate and rendering performance will deteriorate significantly.

Conditional expression (2) defines the focal lengths of the two front lenses, and is for keeping the lens system compact and for maintaining good distortion. If the lower limit of this equation is exceeded and the refractive power of the lens having a negative refractive power of the two front lenses becomes too strong, the back focus becomes long and the lens system becomes large. On the contrary, when the upper limit of this expression is exceeded and the refractive power of the lens having a positive refractive power of the two front lenses becomes too strong, the positive distortion becomes large especially in water,
Not preferable.

[0010]

EXAMPLES Examples of the present invention will be shown below. In the table, f is the focal length of the entire system, F is the F number, ω is the half angle of view when used in air, R is the paraxial radius of curvature, D is the axial upper surface spacing, and N is d.
Refractive index for line, ν is Abbe number.

In all of the embodiments of the present invention, two lenses having refractive powers different in sign from each other are arranged in front of a lens system of positive, negative, positive and negative, consisting of four groups and four elements. It goes without saying that the same effect can be obtained when two lenses having refractive powers having mutually different signs are arranged in front of the lens system having the configuration.

(Embodiment 1) FIG. 1 shows a sectional view of a first embodiment of the present invention, which is a lens system having the lens construction and the conditional expression values shown in the following table.

[0013]

[Table 1]

FIG. 5 shows an aberration diagram in air of the first embodiment, and FIG. 6 shows an aberration diagram in water.

(Embodiment 2) FIG. 2 shows a sectional view of a second embodiment of the present invention, which is a lens system having the lens configurations and the conditional expression values shown in the following table.

[0016]

[Table 2]

FIG. 7 shows an aberration diagram in the air of the second embodiment, and FIG. 8 shows an aberration diagram in the water.

(Embodiment 3) FIG. 3 shows a sectional view of a third embodiment of the present invention, which is a lens system having the lens configurations and conditional expression values shown in the following table.

[0019]

[Table 3]

FIG. 9 shows an aberration diagram in the air of the third embodiment, and FIG. 10 shows an aberration diagram in the water.

(Comparative Example) FIG. 4 shows a sectional view of a comparative example to be compared with the embodiment of the present invention. A conventional example in which a plane plate is arranged is shown, and the lens system has a lens configuration shown in the following table.

[0022]

[Table 4]

FIG. 11 shows an aberration diagram in air of a comparative example,
FIG. 12 shows an aberration diagram underwater.

[0024]

According to the present invention, only two lenses satisfying the conditional expression of the present invention are provided in front of a lens system which is satisfactorily corrected for aberrations in the air, and a good depiction performance is obtained both in air and in water. The resulting amphibious lens system will be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the present invention.

FIG. 3 is a sectional view of a third embodiment of the present invention.

FIG. 4 is a cross-sectional view of a conventional example as a comparative example.

FIG. 5 is an aberration diagram for the first embodiment in air.

FIG. 6 is a diagram of aberrations in water of the first example.

FIG. 7 is an aberration diagram of the second example in air.

FIG. 8 is a diagram of aberrations in water of the second example.

FIG. 9 is an aberration diagram in air for the third example.

FIG. 10 is a diagram of aberrations in water of the third example.

11 is an aberration diagram of the conventional example shown in FIG. 4 in air.

12 is an aberration diagram in water of the conventional example shown in FIG.

Claims (1)

[Claims] 1. A first lens, a second lens, and
And a subsequent lens group, wherein the first lens and the second lens have refractive powers having opposite signs, and satisfy the following conditional expression. system. _{10 <ν P -ν N <60} (1) 0.7 <| f N / f P | <1.3 (2) However, [nu _P: first lens, of the second lens, the lens having a positive refractive power Abbe Number ν _N : Abbe's number of the lens having a negative refractive power of the first lens and the second lens f _P : Focal length of the lens having a positive refractive power of the first lens and the second lens f _N : Of the first lens and the second lens, the focal length of the lens having a negative refractive power