JPH03127006A - Wide converter lens - Google Patents

Abstract

PURPOSE:To shift the focal length to the wide side with a large variable power ratio and to compensate the power chromatic aberration excellently by assuming a negative lens as a 1st lens, a lens having weak negative refracting power as a 2nd lens, a negative meniscus lens as a 3rd lens, and a positive lens as a 4th lens to meet specific requirements. CONSTITUTION:The lens consists of the 1st negative lens which has its concave surface on the image side, the 2nd lens which has much smaller refracting power than the 1st lens, the 3rd negative meniscus lens which has its concave surface on the object side, and the 4th positive lens which has its convex surface on the image side in order from the object side, and constituted to meet the requirements shown by inequalities I - V. In the inequalities I - V, f1, f2 and f4 are the focal lengths of the 1st, 2nd, and 4th lenses, r3 and r4 the radii of curvature of the object-side and image-side surfaces of the 2nd lens, r7 and r8 the radii of curvature of the object-side and image-side surfaces of the 4th lens, phi2 the image-side surface refracting power of the 1st lens, and phi2 the object-side surface refracting power of the 2nd lens. Consequently, the variable power ratio of the whole system is about X0.65 and the zoom ratio is about X8; and various aberrations are compensated excellently and the size and weight are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compact and high-performance wide converter lens that is attached to the object side of a zoom lens such as a video camera and shifts the focal length range of the zoom lens in the wide direction.

Regarding the wide converter lens, which is attached to the object side of the main lens of a video camera, etc. and shifts the focal length to the wide direction while fixing the focal position of the entire system, Japanese Patent Application Laid-Open No. 59-2
No. 04817, JP-A-62-87923, JP-A-63
-100414 and Japanese Unexamined Patent Publication No. 63-253319. The wide converter lenses disclosed in JP-A-59-204817 and JP-A-62-87923 have a large number of lenses (5) and are heavy; When the converter lens is attached and the focal length of the main lens is shifted, the focal length of the entire system is 172 inches, which is insufficient for widening the lens with seven wheels. In addition, it is assumed that the main lens is a single focus lens, so even if the above main lens is zoomed and good performance is again ensured up to the telephoto range, there will be no performance deterioration when the above converter lens is attached. do not have.

Similarly, the wide converter lens disclosed in Japanese Patent Application Laid-Open No. 63-253319 assumes a single focus main lens, so
When attached to a zoom main lens, performance deterioration is unavoidable.

The present invention is attached to the object side of the main lens, which is a zoom lens, and shifts the focal length of the entire system to the wide side with a relatively large magnification ratio of 0.65x, effectively correcting various aberrations, especially lateral chromatic aberration. The objective is to provide a wide converter lens with

In order to achieve the above object, the wide converter lens according to the present invention is attached to the object side of the main lens, which is a zoom lens, to widen the focal length of the entire system to about 0.65 times. The first lens is a negative lens with a concave surface facing the side, the second lens has a sufficiently weak negative refractive power compared to the first lens, the third lens is a negative meniscus lens with a concave surface facing the object side, and the convex surface faces the image side. The fourth lens is a positive lens, and is characterized by satisfying the following conditions.

f.

0.0 <-< 0.6 (1) 2 4 -1.2 <-< -0,6 (2) I 4 0.3 <-< 3 (3) rko10, 8 <-<0 .2 7 (4) However, focal length of the positive lens with the convex surface facing the image side, f2: focal length of the second lens, f,4: focal length of the fourth lens, r object side curvature of the second lens Radius, r: Image side curvature radius of the second lens, r7: Object side curvature radius of the fourth lens, r1 Image side curvature radius of the fourth lens, φ2: Image side refractive power of the first lens, φConi-th Object side refractive power of two lenses.

In the present invention, by making the second lens a sufficiently weaker negative lens than the first lens, in other words, by making the second lens bear some of the negative refractive power of the first lens,
Image plane fluctuations when a converter lens is attached to the main zoom lens can be made smaller over the entire zoom range than when using only a lens. In addition, by making the third lens a negative meniscus lens with a concave surface facing the object side, the first lens can effectively compensate for the positive spherical aberration that occurs in the telephoto range, and furthermore, the image plane tilts toward the over side in the telephoto range. It is possible to reduce the width of the curvature of field on the under side that occurs at the middle angle of view in the wide range, and it is possible to satisfactorily correct the image plane over the entire area.

In addition, on the image side of the fourth lens with positive refractive power, the first lens effectively corrects the positive spherical aberration that occurs in the telephoto range, and the first lens corrects the negative distortion that occurs in the wide range. There is.

Condition (1) defines the range of the focal length ratio of the first lens and the second lens. If the upper limit is exceeded and the negative refractive power of the second lens becomes larger than that of the first lens, a large amount of negative distortion will occur in the wide range, making it difficult to correct it.

Condition (2) is the range of the focal length ratio of the first lens and the fourth lens.If the upper limit is exceeded and the positive refractive power of the fourth lens becomes stronger than the negative refractive power of the first lens, the zoom main When attached to a lens, the fluctuation of field curvature is significant and it becomes difficult to correct it well over the entire focal length.Also, if the lower limit is exceeded, the negative refractive power of the first lens becomes the positive refractive power of the fourth lens. If it becomes stronger than the power, a large amount of negative distortion will occur in the wide range, and it will be difficult to correct it.

Furthermore, condition (3) indicates the range of the curvature radius ratio between the object side surface and the image side surface of the second lens. Here, the second lens is a negative meniscus lens with a concave surface facing the object side or the image side.If the negative refractive power of the object side becomes strong beyond the upper limit of 0 condition (3), or if it exceeds the lower limit. When the negative refractive power of the tiam surface becomes strong, negative distortion occurs in a wide range, and it becomes difficult to correct this.

Condition (4) defines the range of the radius of curvature ratio between the object side surface and the image side surface of the fourth lens.If the lower limit is exceeded and the positive refractive power of the object side surface becomes strong, a large amount of coma aberration will occur and must be corrected. If the upper limit is exceeded and the negative refractive power on the object side becomes strong, when attached to a zoom main lens, the field curvature will fluctuate greatly from the telephoto range to the wide range, making correction difficult.

Condition <5> is the range of the refractive power ratio between the image side surface of the first lens and the object side surface of the second lens. If the lower limit is exceeded and the negative refractive power on the image side of the first lens becomes stronger than the positive refractive power on the object side of the second lens, a large amount of negative distortion will occur in the wide range, making it difficult to correct. . If the upper limit is exceeded and the negative refractive power on the image side of the first lens becomes weaker than the negative refractive power on the object side of the second lens, when attached to the zoom main lens, the fluctuation of field curvature will be significant and it will be good over the entire focal length. It becomes difficult to correct.

In the following description, f is the focal length of the entire system, FNO is the open F value, ω is the half angle of view, and - is the converter value for the main lens. The variable power ratio when the lens is attached, ri is i from the object side.
The radius of curvature of the ith lens surface, di is the axial distance between the ith lens surfaces from the object side, ni is the refractive index for the d-line of the ith lens from the object side, and νi is the d-line refractive index of the ith lens from the object side. These are the numbers for the d-line.

Table 5 shows the configuration of the main lens to which the wide converter lenses of Examples 1 to 4 of the present invention are attached. Table 6 shows the relationship between each implementation and conditions (1> to (3)).

Figures 1 to 4 are cross-sectional views showing the lens configurations of wide converter lenses according to Examples 1 to 4 of the present invention, respectively, and Figures 5 to 8 show wide converter lenses according to Examples 1111 to 4 of the present invention as main lenses, respectively. Aberration diagrams in the telephoto range (L), middle range (M), and wide range (-W) when installed; FIG. 9 is a sectional view showing the lens configuration of the main lens in the telephoto range; FIG. 10 is It is an aberration diagram.

As described above, the converter lens of the present invention has a variable power ratio of the entire system of about 0.65 times, a zoom ratio of about 8 times, and satisfactorily corrects various aberrations over the entire zoom range of the main lens. Furthermore, it has a simple configuration with four lenses, making it compact and lightweight.

Table 1 (Example 1) f=5.68~43.04 FNO-1,44~
1.91 2&1-11.1"~71G" s-
0.66 support radius ◆-Top distance
Refractive index (Nd) Dispersion (νd) Table 2 (Example 2) f-5, 85 to 44. '23 FNO-1,44
~1.91 2(a/-10,8@~71.4"
i+-0,68 support radius Shaft top surface spacing
Refractive index (Nd) Dispersion (Sd) Table 3
(Implementation, N5) f-5,66~4194 FNO-1,44
~1.91 2ω-11,2” ~712°
m-0,65 curvature radius Shaft top surface spacing
Refractive index (Nd) Dispersion (Sd) Table 4 (Example 4) f-5,68~40.04 FNO-1,4
4~1.91 2J-12,0°~710"
m-0,66 radius of curvature axis spacing refractive index (Nd) dispersion (νd)
8 1 piece t1.5jD 8 1.00 Table 5C main lens) f-IL75-66.3 FNO-1,44~1
．． 90 2&-7,2" ~ 51.3' support radius
Top surface spacing Refractive index (Nd) I
l&(νd) table

[Brief explanation of the drawing]

1 to 4 are cross-sectional views showing the lens configurations of wide converter lenses according to Examples 1 to 4 of the present invention, and FIG.
Figures (L), (M), (S) to Figure 8 (L), (M), (
S) is an aberration diagram in the tele range, middle range, and wide range when the wide comparator lenses of Examples 1 to 4 are attached to the main lens. Further, FIG. 9 is a sectional view showing the lens configuration of the main lens in the telephoto range, and FIG. 10 is an aberration diagram thereof.

Claims (1)

[Claims] In a wide converter lens attached to the object side of the main lens, in order from the object side, the first lens is a negative lens with a concave surface facing the image side, and has a sufficiently weak negative refractive power compared to the first lens. A wide converter comprising a second lens having a second lens, a third lens being a negative meniscus lens with a concave surface facing the object side, and a fourth lens being a positive lens having a convex surface facing the image side, and satisfying the following conditions. Lens: 0.0<f_1/f_2<0.51 -1.2<f_4/f_1<-0.6 0.3<r_4/r_3<3 -0.8<r_8/r_7<0.2 0.35 <|φ_3/φ_2|<1.0 However, f_1: focal length of the first lens, f_2: focal length of the second lens, f_4: focal length of the fourth lens, r_3: radius of curvature of the object side of the second lens, r_4: Image side curvature radius of the second lens, r_7: Object side curvature radius of the fourth lens, r_8: Image side curvature radius of the fourth lens, φ_2: Image side refractive power of the first lens, φ_3: Object side curvature radius of the second lens. Object side refractive power.